Local residents near Aisha Mosque in Walsall had been evacuated during the bomb scare early this morning but are now being allowed back home.
The police, however, said it had still not been established what the device exactly was.
"The force are taking this extremely seriously. We've launched a full investigation and what's key to this is the public helping us to understand why the item was in the area," Superintendent Keith Fraser of West Midlands police said.
"It was our first priority to make sure the area was safe early on and evacuated homes on a purely precautionary measure.
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"We will open the mosque up later to reassure residents and allow worshippers to return," he added.
The bomb disposal experts had been dispatched to Rutter Street last night following the discovery of a suspicious package on the grounds of the Aisha Mosque.
The item was taken inside the building by a member of the public before emergency services arrived and cordoned off the area around the building.
There have been at least 10 attacks on mosques across Britain in recent months.
The spike in these suspected Islamophobic incidents is thought to be a backlash to the murder of British soldier Lee Rigby on the streets of Woolwich in south-east London last month.
An Islamic centre in Muswell Hill was razed to the ground and a mosque in Grimsby escaped a similar fate after an alleged firebombing soon after the soldier's killing on May 22.