Website ufosightingsdaily.com posted images taken by the Curiosity rover droid, which is exploring the Red Planet taking pictures for NASA and beaming them back to Earth.
The site said the image showed an alien lizard on the vehicle.
In an article entitled “Lizard Crawling On @NASA Mars Rover This Week, March 2017,” the website’s editor Scott C Waring, said: “This little lizard was holding on for dear life on the Mars Curiosity rover’s camera.
“The animal looks a lot like a lizard with a tall fin back… much like one type of dinosaurs here on Earth… just much smaller.”
He claimed in another image taken by the rover just 10 minutes later, showed the creature had jumped off.
He added: “The photo of before and after is about 10 minutes apart so it is enough time for the animal to have crawled to a new location on the other side of the camera arm.
“This is 100 per cent real proof that alien life, albeit small…does exist on Mars…and at the moment…exists on the Mars rover.”
But, Mr Waring, who is convinced Mars is populated by a menagerie of creatures which resemble animals found on Earth and pint-sized alien humanoids, according to many of his posts, has been left red-faced after fellow UFO investigators examined his claims.
Sceptics rubbished his claim the “lizard” was 100 percent proof of alien life on Mars.
Mick West, administrator of Metabunk.org, a website which investigates and exposes hoax UFO and alien sightings, concluded the alleged lizard was simply a dust removal device at the head of the rover.
He provided close up images of the tool in place on the rover compared the “lizard” in Mr Waring’s post, and they appear to be an exact match.
Mr West said it was another case of pareidolia, a phenomenon when the brain tricks the eyes into seeing familiar objects such as faces or animals in textures or patterns.
Mr West wrote: “An an amusing example of pareidolia, a youtube poster claimed to have spotted a lizard jumping onto the Mars Curiosity Rover
“In fact what he has seen is the dust removal tool.”
Scott Brando, a fellow sceptical UFO investigator said the case had now been officially debunked.
Express.co.uk has contracted Mr Waring and awaits his response.