The statue, which weighs 490kg, is positioned close to where Mandela took his first steps to freedom on February 11 1990 after spending 27 years in jail. The prison was formerly called Victor Verster.
The cover was removed by Mandela's ex-wife, Winnie Madikizela-Mandela, their daughters Zindzi and Zenani and his wife Graca Machel.
Mandela did not speak at the ceremony but appeared visibly pleased with his latest 90th birthday gift from the Sexwale Family Foundation.
Tomorrow, the final celebration takes place in a concert at the Johannesburg Stadium that features music legend Jonas Gwangwa and Senegalese singer Baaba Maal.