A young person in Bangor brought a suspected World War Two device home after finding it in a forest in the Newtownards area.
Police said they were attendance at the Lisnabreen area of Bangor following the discovery.
The device, which was found in Newtownards earlier on Sunday, has been taken away to be made safe by the relevant agencies.
UUP MLA Alan Chambers said: "PSNI in Bangor reporting find of a wartime grenade found in a forest in Newtownards today and brought home by the young finder to his home in Lisnabreen area of Bangor.
"Understand it's being dealt with by army bomb squad. Grateful as ever for their expertise in such situations."