The court in Casablanca convicted Mourtada of "usurping the identity of HRH Prince Moulay Rachid" and "falsification of computer documents", according to Morocco's official MAP news agency.
'Help Fouad'
Mortada said he set up the account on the social networking site in mid-January out of admiration for Moulay Rachid, who is second in line to the throne.
He said he was arrested on February 5, blindfolded and taken to an unknown building where he was beaten and insulted, according to a website set up by his supporters.
But a source close to the Moroccan security services denied Mortada was tortured.
The website alleges the police wanted to establish if there was a relationship between Fouad and terrorist groups seeking to harm the royal family but found no such link.
"It was just a joke, a gag," Fouad was quoted on the site,, as saying: "I regret my gesture and beg forgiveness from my whole family for the harm that I have caused them."
Ilyas, Mortada's brother, said the family would appeal.