North Yorkshire Police say that more than 1,000 people will be moved from their homes in the hamlets of Ebberston and Allerston this afternoon before the 500-pound (225 kilogram) explosive is made safe.
The villages are about 240 miles (385 kilometers) north of London.
The device was discovered Sunday by enthusiasts who are digging up the remains of a plane that crashed in the area in 1940.
Britain was the site of fierce air combat during World War II and unexploded bombs and anti-aircraft shells turn up periodically across the country.
