The Newsroom actress could be seen lying topless on a bed in the image, while wearing a pair of oversized glasses. The picture has since been removed from her Twitter feed.
Pill - who plays Maggie, an associate producer of the news programme at the centre of The Newsroom - has admitted to the error.
She posted on the micro-blogging website after the incident: "Yep. That picture happened. Ugh. My tech issues have now reached new heights, apparently. How a deletion turned into a tweet... Apologies."
Pill's fiancé, actor Jay Baruchel - who the picture is thought to have been intended for - also addressed the incident on Twitter.
He wrote: "My fiancée is an hilarious dork. #imustgladitdidnthappentomefirst."
According to the Los Angeles Times, Pill had around 2000 new Twitter followers by Wednesday afternoon.