Ashton Kutcher and Mila Kunis: Friends with Benefits?

Kunis calls dating rumors "absurd" but a source tells PEOPLE, "They're just friends having fun"

Photo: Jon Kopaloff/FilmMagic; Kristina Bumphrey/Startraks

Ashton Kutcher and Mila Kunis are longtime friends – but are they friends with benefits?

Kunis tells Extra in a new interview from CinemaCon, “A friend is a friend.”

And the actress shoots down rumors that the two are dating, saying, “It’s absurd.”

Still, one source close to Kutcher says the former That ’70s Show costars – who just spent a cozy weekend together in Carpinteria, Calif. – are enjoying spending time together, but not ready for a serious relationship.

“They’re both single, having fun,” the source tells PEOPLE. “There’s nothing serious going on – just friends having fun.”

It should be noted that both Kutcher, 34, and Kunis, 28, have some onscreen experience with relationships that morph between friendship, romance and more. Kunis costarred in Friends with Benefits with Justin Timberlake, while Kutcher appeared with Natalie Portman in No Strings Attached about a pair who have a physical relationship that turns more serious.

Another source told PEOPLE that Kutcher, who recently split from Demi Moore, “was so in love with [Mila] for a while when they worked together. … It never happened, but I’m not surprised by this – at all.”