Three-inch mortars were used during World War II by Australian forces.
WA Police requested Defence assistance to clear the “unexploded ordnance”, which was found by a member of the public on vacant land next to Hepburn Avenue.
The object was found to be inert and was removed for disposal.
An ADF spokesman said he would not provide details about testing and removal due to operational security reasons.
He advised anyone who found a suspicious item that might be unexploded ordnance to not touch or disturb it, but contact the police who would arrange for military experts to dispose of it.