An Air France flight from San Francisco to Paris was diverted to Montreal "as a precaution" after an "anonymous threat".
Flight AF083 from San Francisco to Charles de Gaulle touched down just before midnight local time in Montreal (5am Irish time), the firm said.
"An investigation will be carried out by the authorities to identify the origin of the alert," Air France said in a statement to AFP.
The airline apologised for the "inconvenience and delay" to its passengers.
France has been on high alert since an attack in Paris on 13 November in which 130 people died.