Al Jazeera's Bernard Smith, reporting from Johannesburg, South Africa's commercial city, said "it looks like the beginning of the end for Thabo Mbeki".
He quoted the ANC's secretary general as saying that when the party told Mbeki what it had decided, his reaction was normal and that he didn't display any shock or any depression.
Mbeki agreed that he was going to take part in the processs to remove him as president, said Smith, quoting the ANC official.
"It seems like Mbeki is not going to fight this," he said.
"It looks like he is going to end up resigning and then parliament will appoint a new president who will be in place until scheduled elections are called as early as April - between April and June - next year."
The ANC had appeared unable to reach a decision on the issue at a meeting on Friday and cancelled a news conference where officials had been scheduled to announce their decision.
"The debate is actually in the middle of nowhere. Everybody is expressing their view and then when we complete that debate and take a decision we will come and communicate with you," Gwede Mantashe, the ANC secretary general, said.
Following the ruling in Zuma's trial, the ANC youth league called for Mbeki to leave but the ANC as a whole reacted more cautiously, saying any decision would be by consensus and announced after its national executive committee had met over the weekend.
Half the cabinet is reportedly threatening to walk out if Mbeki is forced to leave.
The president issued a statement on Friday saying: "It impoverishes our society that some resort to the tactic of advancing allegations with no fact to support these.
"The question will have to be answered now - what kind of society are we building, informed by what value system and with what long-term effect to the political and overall moral health of the nation?"
Mbeki took over as South Africa's president in 1999.
The dismissal of corruption charges against Zuma makes it possible for him to become South Africa's president after next year's election.