The young African woman first saluted the statue of the former president, who is revered for his role in defeating the racist apartheid system, before disrobing, witnesses said.
A picture posted on Twitter showed her naked and leaning her head against the knee of the statue in an upmarket area of South Africa’s commercial capital.
A waitress at a nearby restaurant told The Star newspaper that the woman’s actions, at around 4.00pm on a busy Monday, had caused a frenzy.
Male waiters got their orders wrong and a male customer was hit on the head by his wife for getting up to take a closer look, she said.
Nelson Mandela Square marketing manager Megan Meas said a security guard had asked the woman to put on her clothes, which she did before leaving the square without answering any questions.
“This was an unauthorised incident conducted by a private citizen in her personal capacity on our property,” Meas said.