The 90210 star has since cropped the photograph, which initially included a shot of her nipple. McCord apparently intended to dedicate the picture to one of her followers.
"This is for you @meganraee You rock!," she wrote, including the Twitpic.
The star then appeared to realise the mishap and cropped the picture before re-posting it.
Her fan responded to what appeared to be a private message from McCord confirming that the nipple had indeed been cropped out.
"I can't reply in a message since you don't follow me, but yes its gone!! I wasn't sure if you noticed it when you posted," wrote the fan.
The actress is currently dating Dominic Purcell.
She was previously in a relationship with Twilight star Kellan Lutz, but the two ended their romance in 2011.