The Scream 4 actress, who has been dating fellow actor Evan Peters, 26, for a year, was staying at a hotel in Vancouver at the time of the incident.
Police were called to their hotel on July 7 after guests heard the couple fighting. Evans was found with a bloody nose and a bite mark whilst Emma appeared unharmed.
But despite Roberts arrest, she was released just hours later as Evan refused to press charges against her.
According to a source, the pair were both hitting each other, with Roberts being arrested as Peters had obvious physical injuries.
The pair are now reportedly back together and are working on Peter’s hit show American Horror Story, which is now in it’s third season.
They have been pictured in frequent public displays of affection since they began dating last year, after meeting on the set of the film Adult World. Just weeks ago they looked loved up and happy as they posed for a picture at The Lone Ranger premiere.
Peters has previously referred to his girlfriend as ‘the love of my life.’
Both parties representatives have declined to comment.