The United States government has told Adam Habib, a professor at the University of Johannesburg and a well-known political commentator, not to come anywhere near its star-spangled shores.

Habib, the vice-chancellor of research and innovation at the university, and his family have been denied entry to the US in terms of a section of the country's immigration act that makes it clear that Habib is a terrorist.

For this reason - because I don't want inadvertently to detonate anything - I ring the doorbell at Habib's Saxonwold, Johannesburg, home very gingerly.

And after Habib, 42, lets me into the house, I peer carefully under his motor vehicle and in the garden for signs of a bomb-making enterprise. But there's nothing to be found.

"Yes, yes, according to the United States, this would apparently be the locus of terror in this area, so check it out," said Habib, and continued palavering on his mobile telephone to a foreign news agency about the Jacob Zuma appeal.

I remember that one famous terrorist carried a bomb in his shoes, but I can't check Habib's because it's a hot afternoon and he is not wearing any. There also seems to be nothing unusual about the contents of the cup of tea he makes me before we start talking on the stoep.

The only suspicious person in the house is a small one wearing spectacles and peering intently at a flickering TV screen.

This turns out to be Habib's son, Irfan, 11, who has also been refused entry to the US, along with eight-year-old Zidaan, his younger brother, and Fatima, his mother.

Last year, Habib was deported from the US after landing in New York en route to addressing a conference of the American Association of University Professors (Aaup).

About a decade or so previously, Habib had lived in New York City for three years completing his doctorate at City College of New York.

This year the American Sociological Association invited Habib to an August conference in Boston; Arnova, a civil society grouping, invited him to address a November conference in Atlanta; and the Aaup invited him to speak to a 2008 conference. So that he could address the conferences, Habib, with the help of the American Civil Liberties Union (ACLU), applied in May for a review of last year's deportation and a new entry visa to the US.

About 10 days ago, he received a reply, dated October 26, from Charles Luoma-Overstreet of the US consulate-general in Johannesburg, informing him that in terms of section 212(a)(3)(B)(i)(I) of the US immigration act, he would not be allowed entry into the US - and that there was no point in appealing the finding because an appeal would be turned down.

The act, a copy of which was sent to Habib, states that "any alien who has engaged in terrorist activity" may not be given entry into the US.

"I have no idea what this is about," said Habib, who was born in South Africa.

"At first, I thought it was a case of mistaken identity - the name Habib is extremely common in the Middle East, it's like being called Smith - and then I thought it was because I had written certain papers critical of the US. But I know other people who have common 'Middle Eastern' names and who have been critical of the US, and yet they have not been denied entry.

"In addition, my family has also now been denied entry - we're talking about two children aged 11 and eight."

Habib said he was then told by a highly placed South African government official that his exclusion was apparently related to photographs taken of him addressing an anti-Iraq war rally in Durban.

"But the strange thing about that is that I know other people who addressed the same rally, and also had their pictures taken, and they, too, have not been denied entry."

He said that he had "of course" exchanged e-mails with Muslim scholars worldwide: "In the course of my job, I get about 70 e-mails a day from a variety of scholars from all over the world, Jewish ones, Islamic scholars, Christians, Marxists, neo-conservatives, fascists, deists - you name it".

Habib said that, in terms of Muslim practice, he also gave charity ("zakat") to various organisations.

"But I'm pretty careful about where I send my money and I focus on education and HIV/Aids in South Africa. I have also given to the Gift of the Givers, but they operate in co-operation with the department of foreign affairs - so if the US government wants to suggest that the department is also a terrorist organisation, well."

Habib said that, as far as he could tell, his exclusion from the US seemed to be the result of a mixture of "racial profiling" - "I'm a Muslim, after all" - and what the American Civil Liberties Union calls "ideological exclusion".

"It's scary. These days if the US government doesn't like what you say, or the views you apparently hold, well, it just won't let you in.

"But I think," Habib said, "the problem is much bigger than the case of Adam Habib and I think it's pretty serious - and that it's time our government did something about protecting its innocent citizens from being targeted and labelled in this way."

Habib said he had encountered a number of people who were targeted for no apparent reason.

"I have been told of a Canadian dentist of Muslim extraction who was whisked out of New York to Guantanamo Bay. It was all a big mistake, but it took his family nine months to get him out - and he was completely traumatised by then.

"You know, the constitutional court recently found that our government had an obligation to make sure that the mercenaries in Africa were not tortured, murdered, etc. How much more so does our government have a duty to its citizens - those falsely accused - and others?"