Mr Mugabe told Mr Zuma in a phone call that he was fine, the South African leader's office said.
Troops are patrolling the capital, Harare, after they seized state TV and said they were targeting "criminals".
The move may be a bid to replace Mr Mugabe with his sacked deputy, Emmerson Mnangagwa, BBC correspondents say.
Mr Mnangagwa's dismissal last week left Mr Mugabe's wife Grace as the president's likely successor.
Please subscribe HERE http://bit.ly/1rbfUog
World In Pictures https://www.youtube.com/pla...
Big Hitters https://www.youtube.com/pla...
Just Good News https://www.youtube.com/pla...
Channel BBC News