Mugabe, the only ruler the southern African nation has known since it was recognized in 1980, delivered the same speech he gave on 25 August, pinning his hopes on China to help revive Zimbabwe's struggling economy.
Mugabe finished the speech without interruption on Tuesday and his spokesman blamed officials, adding the president would read the correct speech at a later date, Reuters reports.
"The mix-up happened in his secretarial office. Therefore the delivery in Parliament should be set aside," spokesman George Charamba was quoted as saying by the online edition of the government-owned Herald newspaper.
But the main opposition Movement for Democratic Change (MDC), which is critical of Mugabe's long rule, said the blunder called into question his fitness to hold office.
Mugabe shows no visible signs of illness and has denied reports that he suffers from prostate cancer. He has dismissed a fall at Harare airport on 4 April as a simple slip.
"This is a historic blunder. Anyone who is still of a sound mind would have quickly picked it up that the speech was the wrong one," MDC spokesman Obert Gutu told Reuters.
"But it dovetails with what we in the MDC have been saying that Robert Mugabe is no longer fit for purpose. He should resign," Gutu said.
Earlier parliament suspended live television and radio broadcasting of Mugabe's speech after the MDC threatened to disrupt the event.
The opposition booed and heckled Mugabe about the deteriorating economy during his last speech in August.
MDC member of parliament Innocent Gonese told parliament that the MDC would disrupt proceedings to protest against anonymous death threats to opposition MPs if they heckled Mugabe again.
Speaker of parliament Jacob Mudenda, however, warned the MDC they would face contempt charges. Broadcasting was then suspended before Mugabe started his speech.
During the speech, the MDC members sat quietly, while ruling ZANU-PF party supporters clapped at regular intervals.
Mugabe arrived at parliament in a vintage black Rolls-Royce car with his wife Grace, and inspected a guard of honour. The 91-year-old leader was also treated to a fly-past by three fighter jets and to a 21-gun salute.