He did so without the lavish parties that marked the occasion during his nearly four-decade rule.
An intelligence official who follows Mugabe's movements said the former ruler was at his Blue Roof mansion with wife Grace and had no known plans to leave the compound.
During Mugabe's rule, his birthday was marked by lavish fetes thrown by his ruling Zanu-PF party, where loyalists would feast on dishes ranging from elephant to buffalo meat.
State companies and government departments traditionally marked the event by placing fawning advertisements in the country's state-controlled newspapers, while office staff would pamper Mugabe with presents.
Since Mugabe left power, the government has declared his birthday a public and bank holiday, Robert Gabriel Mugabe Youth Day. The man who ruled Zimbabwe from independence in 1980 has himself not been seen or spoken in public since stepping down.
"Who cares about Mugabe now?" said Tendekai Savanhu, a street vendor and avowed opposition supporter. "We don't want to know what he is doing, this country is better off without him."
"He told me that he had resigned for the sake of peace and development of the country and he agreed to go," said Moussa.
Mugabe has defied media reports about his health and has outlived his longtime political nemesis Morgan Tsvangirai, who died last week after a long battle with cancer and was buried in his rural home of Buhera on Tuesday.