People around the world were asked to honor Mandela by devoting 67 minutes of their day to public service - one minute for every year of Mandela's public service.
U.S. President Barack Obama called Mandela "a beacon for the global community, and for all who work for democracy, justice and reconciliation."
Mandela spent his birthday with friends and relatives in his rural hometown of Qunu, some 600 miles south of Johannesburg.
Mandela became South Africa's first black president in 1994 after spending 27 years in prison for his fight against racist apartheid rule. He was later awarded a Nobel Peace Prize for his efforts.
The Associated Press contributed to this report.