The actress - who has previously denied that she is dating her boyfriend in the show Josh Hopkins - posted a picture of her hugging Travis Cobb actor Byrd.
The two were sharing an affectionate clinch as they prepared to wrap up the final day of filming season three of the hit show.
Cox wrote: "'If only we didn't play mother and son... Day before wrapping Season 3 of Cougar Town : ("
The estranged wife of fellow Scream actor David Arquette only recently joined the micro-blogging website and was welcomed by her ex.
He tweeted: "Oh my goodness - It's a miracle. Welcome to twitter Courteney! Don't let the haters discourage you. There's a lot of love 4u."
Cox returns to US screens in new Cougar Town from February 14 at 8.30pm on ABC.
> Courteney Cox: 'Kissing Josh Hopkins in Cougar Town confuses daughter'