"Let him go, he didn't do anything," other protesters yelled as police officers grabbed the man and tried to drag him away from the event.
He momentarily broke free of the officers' grip.
When they caught him again, a CBC reporter heard the man say, "I was joking, there's no bomb," before he was escorted away.
Police later said one man was arrested for "uttering threats," though it is unclear if charges will be laid.
Shortly before Harper's arrival at the Ben Weider Jewish Community Centre, another protester briefly managed to burst into the reception room, repeatedly yelling "Harper, dictator," before security escorted her out.
Mount Royal has voted for the federal Liberal Party for decades, but veteran MP Irwin Cotler chose not to run again, and the Tories think they have a chance at the seat.
Robert Libman, who created the provincial Equality Party in the 1980s and managed to get himself and three others elected to the National Assembly in 1989, is running for the Tories.
After the Equality Party dissolved, Libman served as mayor of Côte St-Luc for eight years.
He will be facing off against the city's current mayor, Anthony Housefather, who is the new Liberal candidate for Mount Royal.
In 2011, Conservative candidate Saulie Zajdel lost to Cutler by 2,260 votes.
Mario Rimbao, a fleet operator for the shipping company FedNav International, is running for the NDP in the riding.