In a series of Tweets the former reality star outlined the alleged sexual encounters with the Entourage star.
"Hey @jeremypiven! ‘Member when you cornered me in your trailer on the #Entourage set? ‘Member grabbing my boobies on the 🛋 without asking??," her first Tweet reads.
A third tweet from the actress says, "Jeremy Piven, on two occasions, cornered me & forcefully fondled my breasts & bum. Once at the mansion & once on set."
Bellamar also alleges that Piven sent her abusive messages.
Piven currently stars on CBS programme Wisdom of the Crowd, and the TV network have confirmed that they are looking into the allegations.