Zuma defeated Mbeki at an acrimonious party election in December and
is likely to become the country's president when Mbeki steps down in 2009.
But the ANC president must first have corruption charges against him cleared.
He still faces trial on money-laundering and racketeering charges and if found guilty, he could be imprisoned.
Asked by the Financial Times if Mbeki and most government ministers had a "straitjacket" around them, Zuma responded: "The president himself and the ministers' term have to come to an end, and therefore that in itself tells you more where the power lies."
The rivalry between Zuma and Mbeki has plunged the ANC into the worst internal crisis in its history, creating two centres of power between the government and the ANC.