Rescue crews attended the scene and helped people climb down a ladder from the second-floor window on to the roof of a fire engine. A large crowd of onlookers gathered to watch at the Ram Allah scene.
Officials said one side of the building was damaged on three stories, though details on the extent of the damage were not available. There were no immediate reports of injuries, and the fire was under control.
The parliament's secretary-general, Mahmud al-Ramhi, said: "The fire caused some material damage, but there have been no casualties. All the staff were swiftly evacuated."
Yazid Abu Einayah, in charge of electrical maintenance at the parliament, confirmed that the fire had been set off by an electrical fault.
"The fire broke out in an electricity panel on the ground floor and then spread to other electricity boxes," he said.
Aziz Dweik, a member of Hamas, refused to rule out the possibility of arson.
"We must refrain from launching allegations as it is obvious to everyone that it was an electrical short-circuit"
Fatah member of parliament
"This is a very serious incident," he said. "We are going to form a commission of inquiry to investigate the circumstances and will ask the security services to do the same thing.
Dweik then voiced suspicions that "someone in the pay of the Israelis or Americans" could have been behind the blaze.
Abdullah Abdullah, an MP for the opposition Fatah faction, said: "We must refrain from launching allegations as it is obvious to everyone that it was an electrical short-circuit."