The `Charlie`s Angels` actress has reportedly embarked on a low-key romance with the baseball star - who is nicknamed `A-Rod` - after they met at a Creative Artists Agency Super Bowl party in February.
A source told Life and Style magazine: "-A-Rod` is with Cameron. They`ve been keeping it quiet, but they`re totally together."
The relationship is still in its early stages and is said to be "casual" with neither the sportsman or Cameron looking for a serious commitment.
It was previously reported that the 37-year-old actress had been dancing and "grinding" with Alex, 34, at the Super Bowl party.
The New York Yankees player was sitting on a couch beside Cameron as she "was dancing by herself" before moving her gyrating body towards him.
At one point the blonde beauty - who was "tipsy" and being very "fun and flirty" - began "grinding on `A-Rod`".
Alex has been single since splitting from actress Kate Hudson in December.
Cameron has previously dated a host of famous men including Maroon 5 star Adam Levine, musician John Mayer and British model Paul Sculfor.