It happened around 4pm on Tuesday afternoon and involved a Black Kawasaki motorcycle that left the road and came to rest on moorland.
The rider, a man in his 30s, was air-lifted to James Cook Hospital in Middlesbrough for treatment.
Officers are appealing for witnesses to the collision or anyone who recalls seeing the motorcycle prior to the collision, to get in touch as soon as possible to assist the investigation.
Please quote the North Yorkshire Police reference number 12210088343.
The stretch of road was closed for four hours while officers investigated the scene and to allow the motorcycle to be recovered.