In a statement, Mthethwa said he was "shocked" by the death of legendary pop star and saluted him for partaking in the 1988 "Free Mandela Concert".
"We salute George Michael for supporting our cause for freedom and for playing at the Free Nelson Mandela Concert to mark Tata Nelson Mandela’s 70th birthday, which was held at Wembley Stadium, London in June 1988," Mthethwa said.
"This concert raised worldwide consciousness of apartheid and the imprisonment of Madiba and other freedom fighters by the apartheid government."
Mthethwa also said Michael was a champion for the rights of lesbian, gays, bisexual and transgender people by living his life openly.
"George Michael stood up for LGBT rights. He championed the rights of artists and fought for ownership of his music," Mthethwa said.
Michael's best-selling hits include the 1984 song, "Careless Whisper" which he did as part of the pop duo called "Wham" in the 1980s.
He had a hugely successful solo career and collaborated with artists like Elton John and Aretha Franklin. Michael's solo album "Faith" sold more than 25 million copies worldwide. He sold more than 100 million records in his career.
Michael, whose real name was Georgios Kyriacos Panayiotou, also courted controversy with his drug use, car accidents and other indiscretions.
Mthethwa said: "We shall continue to play his music and still see his image on the silver screen."