The former president and anti-apartheid leader was admitted to a hospital in Pretoria, the capital, on Saturday.
"The doctors have completed the tests," presidential spokesman Mac Maharaj said in a statement. "He is well and as before, his health remains under the management of the medical team."
Maharaj appealed to the public and media to respect the privacy of 94-year-old Mandela and his family.
The African National Congress, South Africa's ruling party, had earlier released a statement saying it believed Mandela was in "capable and competent hands."
Mandela, who has become increasingly frail in recent years, was hospitalized for nearly three weeks in December. At that time, he was treated for a lung infection and had a surgical procedure to remove gallstones.
Under South Africa's white-minority apartheid regime, Mandela spent 27 years in prison before he was released in 1990. He became the nation's first democratically elected president in 1994 under the banner of the African National Congress. He served one five-year term before retiring.