Officers in Pontefract found the vehicle, which at first glance looks just like a bicycle, which had been adapted with a petrol engine.
The changes meant that it was illegal to ride the bike on a highway 'as a typical off road motorcycle', and the vehicle was also being ridden with no helmet or documentation.
The seize happened in Monkhill Lane on Saturday.
-> Pulled over BMW driver avoids arrest for having flashing blue lightsA spokesman for the force said: "On Saturday 5th January officers from the Pontefract Neighbourhood Policing Team seized this bike which was being ridden using the adapted petrol engine around the Monkhill Lane area of Pontefract.
"This may appear to be a pedal cycle however, please be aware that by adapting a pedal cycle in such a way it becomes as illegal to ride on a highway as a typical off road motorcycle. The vehicle was being ridden with no helmet and with no documentation on the highway and was subsequently seized by officers.
"If you adapt a pedal cycle and use the pedal cycle via the petrol powered engine and ride it as such in any public place or on the highway, it is committing the same offences as doing the same on an off road motor cycle.
"The owner will be liable for charges to recover the bike and will be dealt with accordingly in relation to the road traffic offences committed."