A charity shop had to be sealed off when a worker found a grenade in a box of donated items.
Bomb disposal experts were called to the Mencap store in Old Catton, near Norwich, Norfolk, where staff and customers were evacuated.
Police were alerted at about 08:50 BST by a member of staff after they found the suspicious item among donated military goods.
The "old grenade" was declared safe at the scene, a police spokeswoman said.
It was not known how old the device was, she added.
Mencap said it has been removed and the shopping centre reopened.
The Army's Explosive Ordnance Disposal team, from Essex, arrived at about midday and left some 30 minutes later.
Mencap said in a statement: "A member of staff at our shop in The Paddocks contacted the local police regarding an item placed in a donations box.
"All safety procedures were followed.
"The police have now confirmed the item is not a danger or threat to life and it has been removed."
Police said at the time of the scare that they did not believe the donation had been "malicious".