Kristina Hagan has hired top celebrity lawyer Gloria Allred to represent her, and accuses Boreanaz of sending her "sexually inappropriate text messages" in August 2009, when they began filming the crime drama together.
According to the legal papers, obtained by TMZ.com, Hagan shared a car ride with the former Buffy The Vampire Slayer star last September (09) and told her he was "the boss" and could "make things happen for her".
The suit goes on to claim that Boreanaz parked the car and "attempted to kiss her and touch her breasts", only for the actress to push him away.
But her refusal to engage in Boreanaz's allegedly bad behaviour didn't stop the star from continuing - he reportedly "unzipped his pants, pulled out his penis and began stroking it until he ejaculated".
He is said to have repeated his actions in another incident that month, when he is claimed to have fondled Hagan in his trailer before he "masturbated in front of her".
Hagan has also named bosses at the Fox network and the production company behind Bones in the suit, claiming they failed to take preventative action against the star's behaviour.
Boreanaz has yet to comment on the reports.
The legal action will do little to help Boreanaz's efforts to salvage his marriage to former Playboy Playmate Jaime Bergman - the couple is in counselling after he confessed to cheating on his wife of nine years.
The actor revealed in May (10) that he had been unfaithful after a former mistress threatened to go public with their affair.