The onscreen detectives have been spending time together offscreen in L.A.
A show insider tells PEOPLE that the former American Horror Story star, 53, is now romantically involved with the Hawaii-born Nikita actress, 35 – who stars with McDermott on CBS’s new crime drama Stalker.
The onscreen detectives sparked relationship rumors last month when they were spotted getting cozy while shopping in Brentwood.
McDermott ended his 14-year marriage to actress Shiva Rose in 2009. They have two daughters together: Colette, 17, and Charlotte, 9.
Reps for McDermott and Maggie Q could not be reached.