People are asked not to try and help the dog spotted on the Mountain Road.
The dog is thought to be Eddie, who went missing from Ramsey almost a month ago.
Police say the owner is aware and will try to collect him if officers can find him.
Members of the public are asked not to go up to the area and try and help, as it could scare the dog away and can be dangerous to stop on the Mountain.
Could you take over this former restaurant?
Framework of new Sea Services Agreement ready, says minister
Attorney General says he's stepping down
Road closures in two towns for running event this week
Six weekend ferry crossings could face disruption
President of Tynwald announces retirement
Police close Mountain road
Fuel firm says "fingers crossed" for calmer energy costs