Credit: Lester Cohen/; Jim Spellman/

Stop the gossip: Jennifer Aniston isn't heating up with one of her costars in The Bounty Hunter.

"She is not dating Jason Sudekis," her rep tells

Sudekis, 34, who is also on Saturday Night Live, divorced wife, 30 Rock writer Kay Cannon, earlier this year.

Still, Aniston's rep adds, "I have no idea how this rumor got started, but there is no truth to it whatsoever."

On Tuesday, Aniston helped BFF Courteney Cox celebrate her 45th birthday at Bouchon Beverly Hills.

"The group sang 'Happy Birthday' to Courteney," a witness tells Us. "They all seemed to be laughing and having a great time."