Isabelle Tremblay, spokesperson for Montreal's public transit corporation, says the bus caught fire in Dorval while shuttling passengers on the 204 line.
The fire broke out just before noon at the corner of Neptune Boulevard and Parkfield Avenue, not far from Trudeau airport.
No one was injured.
Firefighters put out the fire at the scene and passengers were transferred to another bus, Tremblay said.
Tremblay said it's not yet clear what sparked the fire and the bus will be examined.
In April, another STM bus caught fire while travelling along the Ville-Marie expressway. The transit corporation later blamed the fire on a faulty alternator.