Radar Online quoted a close insider as claiming that the 24-year-old had a wild streak when she was younger and made the alleged video.
"Emma Stone has a sex tape and that's a fact. She made it long before she started dating Andrew Garfield, and before she really became a household name. She was just young and probably thought nothing would ever come of it," a source told the gossip portal.
The homemade video has reportedly not been shopped around yet.
"The tape remains in the hands of the person she made it with. But that doesn't mean there's any guarantee that it won't eventually hit the market. The higher Emma's star rises, the more valuable that tape becomes," the source added.
Stone is currently dating her 'Spider-Man' co-star Andrew Garfield.