The Triumph Trophy TR5 was ridden by Henry Winkler's character Arthur Fonzarelli, better known as Fonzie, in the classic ABC sitcom between 1974 and 1984.
Presumed lost, collectors are expected to rush to a Los Angeles auction house on November 12 to bid for the bike.
According to Autoblog, stuntman Bud Ekins held onto the bike until 1995 before selling it to friend Marshall Ehlers, who was not aware of the Triumph's importance.
The Triumph is expected to fetch more than $90,000 (£57,000) at the auction.
Watch a classic Happy Days clip featuring The Fonz below: