Presidential spokesman Mac Maharaj said 94-year-old Mandela went to a hospital in Pretoria, the capital, Saturday afternoon.
Maharaj says doctors are running tests and have indicated that there is "no reason for any alarm."
Mandela, a leader of the fight against apartheid and a former president, was hospitalized for nearly three weeks in December before going home on Dec. 26. At that time, he was treated for a lung infection and had a surgical procedure to remove gallstones.
The Associated Press contributed to this report.