West Oxfordshire District Council said an online advert on Gumtree promoting the sale of land at Turley Lane in Hailey, Oxfordshire, was not "viable".
It added that permission to develop the land would be highly unlikely.
Warwick Robinson, cabinet member for planning, said steps were taken in 2005 to protect the land from development.
Gumtree is an online site for classified advertisements.
People in Oxfordshire are being warned of a "scam" which claims developers are entitled to purchase an area of greenbelt land for investment.