The grenade fell out of the ceiling at 5 Overdale Rd. according to a contractor who was working on the home. Police and fire officials were called in at about 4 p.m. and later determined it was an actual grenade.
The homeowners say they have no idea how it got there.
The house was built in 1960 "and really hasn't been renovated much" since, Shirley Meisels told CBC News.
Little is known about the previous owner, she said.
Police told CBC News the grenade was live and could have exploded. It was removed by emergency personnel and residents were allowed to return to their homes by about 6 p.m.