There were no injuries.
The Canadian Council on American-Islamic Relations says Gatineau must investigate the attack as a hate crime.
The organization says it is not the first time the mosque has been the target of vandals.
The council says that attacks such as the early morning vandalism in Gatineau divide communities by stigmatizing visible minorities.
It added, however, that it does not believe that the criminal action reflects the viewpoints of most Canadians.
The Gatineau incident was not the only attack in recent days against Muslims. New York police are investigating a series of arson attacks in the Queens borough on Sunday in which one of the targets was an Islamic centre.
New York investigators are looking into the attack as a possible hate crime.
The other targets were a bodega and private homes.