Mugabe has ruled Zimbabwe since independence from Britain in 1980.
Critics accuse the president of human rights violations and say his policies have taken a drastic toll on the economy.
Mugabe attacks critics
Addressing thousands of supporters at the birthday party, Mugabe said his government was working hard to turn around the economy and said his rivals, and Morgan Tsvangirai, leader of the MDC in particular, were sabotaging his plans.
"Morgan Tsvangirai and his MDC, those puppets of the British, are trying to organise to remove us from power to fulfil an agenda given to them by the British," he said.
"But their efforts will come to nought because we have the support of the people of the people and, even if he denounces us from the top of a mountain or appeals for foreign intervention from there, we are not going to fall."
|Morgan Tsvangirai, the leader of the Movement for Democratic Change, criticised the birthday party [AFP]|
But as Zanu-PF laid on a feast for his birthday, the International Monetary Fund (IMF) expressed deep concern over Zimbabwe's deteriorating social and economic conditions.
On Friday the IMF said it would maintain its suspension of financial and technical assistance to Zimbabwe, saying Harare had failed to clear its debt arrears and address the worsening economic and social crisis.
The lavish birthday celebration comes after the government banned political rallies and protests in volatile townships and districts in the capital Harare for three months.
The opposition compared the move to that of a "state of emergency".
On Friday the police cancelled an opposition meeting in Bulawayo, the country's second largest city.
The 3-month ban followed weekend clashes between riot squads and opposition supporters when the police fired teargas and water cannons to stop a major rally.
Mugabe has consistently refused to say when he will cede power and has suggested that colleagues in Zanu-PF were plotting to edge him out.
At its December congress, the ruling party noted a motion to extend Mugabe's rule by two years under a plan to hold both presidential and parliamentary elections in 2010.
The motion is expected to be considered by Zanu-PF's central committee and debated in parliament before the end of the year.