The web address supermario4.com was registered to Nintendo of America on Tuesday, April 3.
The domain purchase could be a simple defensive move on Nintendo's part, with evidence suggesting that the firm could be preparing to announce the title.
The domain name currently redirects to Nintendo's home page.
> Retro Corner: 'Wario Land: Super Mario Land 3'
In January, Nintendo announced that it is currently developing a new 2D Mario game for the Nintendo 3DS that could become Super Mario 4.
Nintendo has avoided numbering the Mario series since Super Mario Bros 3 on the NES.
Nintendo released Super Mario 3D Land on Nintendo 3DS last year, which became the fastest-selling game in the series.
> Digital Spy reviews 'Super Mario 3D Land'
> Digital Spy reviews 'Mario Kart 7'
Watch the trailer for Super Mario 3D Land below: