The incident happened about 1600 GMT on Sunday before a flight departure.
A spokesperson for the airport said passengers were on board while waiting for aircraft to be de-iced.
The flight was the 1445 GMT Amsterdam service.
Passengers were offloaded and the flight was cancelled.
A spokesperson for Easyjet said:
"EasyJet can confirm that flight EZY6773 from Belfast to Amsterdam on 20 November was cancelled due to a technical issue resulting from an airport vehicle accidentally hitting the aircraft during boarding.
"The safety and wellbeing of our passengers and crew is always easyJet's highest priority.
"The Captain kept the passengers informed and they were given the option of being rebooked onto the next available flight or obtain a refund.
Passengers were offered meals and hotel accommodation if they needed it.
The company apologised for any "inconvenience caused."
An Easyjet aircraft has collided with a de-icing vehicle at Belfast International Airport.