There was no immediate update on his health Thursday, but President Jacob Zuma on Wednesday reported that Mandela was responding better to treatment for a recurring lung infection.
Grandson Mandla Mandela said Wednesday that the family is appreciative of the support it has received from around the world.
The leader of South Africa's anti-apartheid movement, Mandela spent 27 years in prison during white racist rule. He was freed in 1990 and became South Africa's first black president in 1994.
Mandela's official Twitter feed noted that Thursday was the 49th anniversary of the former president's arrival at Robben Island, the prison off the coast of Cape Town where he spent the majority of his incarceration.