"What Mbeki has said is nothing new other than what he said in December when he visited Harare," a spokesman for the opposition Movement for Democratic Change (MDC) William Bango said.
Speaking on behalf of the MDC leader Morgan Tsvangirai, Bango reiterated the party had always been ready for talks.
The MDC reaction came soon after the South African president announced the party had agreed for talks with Mugabe's government to resolve the country's political crisis.
"I am pleased to say the two sides have agreed to enter into formal negotiations. They will soon enter into formal negotiations," Mbeki said.
But Zimbabwean opposition leaders were quick to point out Mbeki's announcement was not new.
"It’s a position which was communicated to him during his visit in December, but there is nothing on the ground that has taken place here," Bango elaborated.
"What Mbeki has said is nothing new other than what he said in December when he visited Harare."
Movement for Democratic Change
Another MDC official, Nkanyiso Maqeda said the party had always been ready for dialogue and "what remains is for President Mugabe to formally say he is ready for dialogue."
Mbeki's announcement elicited no immediate response from Mugabe's camp.
Zimbabwe has slipped into political turmoil with the opposition accusing Mugabe of rights abuses and gross economic mismanagement. The opposition has also challenged Mugabe's presidential re-election in 2002.
Amid soaring inflation and rampant unemployment, the country witnessed an outpouring of street protests months ago.
Mugabe put down the protests with a heavy hand. Opposition leader Tsvangirai has been thrown in jail, charged with plotting to overthrow the government.
South Africa and Nigeria brokered talks between the government and the opposition in May 2002, but they soon collapsed.