The short clip uploaded to YouTube shows the pedals turning on just one bike in a row of a number of them inside a health club in Mexico.
The pedals appear to turn at a fixed speed, rather than slowing down as if someone had just got off.
No one is sitting on the machine, and nothing is apparent that could be rotating them, so some people suspect it could be a ghost.
The video “Poltergeist caught on tape – real – in health club” was uploaded by YouTube channel Strange Videos.
A promotional blurb for the video says: “This video shows what some people believed was a poltergeist or an invisible person using an exercise machine in a health club in Mexico.
“The clip shows the bike pedalling all by itself as if someone invisible was using it, the pedals seem to slow down only for them to speed up again.”
No details have been given of the location of the gym.
Viewers have joked about the video.
One said: “Even spirits have to stay in shape!”
Another said it had been hoaxed using a hamster.
He said: “Hamster in the wheel hub! Nice try though.”