In the sci fi world Kellerman is perhaps best known for her role as Dr. Dehner (a psychologist) in the second crafted pilot episode for Star Trek: The Original Series. In this episode, she and her love interest, Gary Mitchell, played by Gary Lockwood (of 2001: A Space Odyssey fame) attain telepathic and telekinetic powers after the Enterprise passes through an energy barrier at the edge of the Galaxy. Their powers eventually become so strong that they feel god-like and attempt to take over the Enterprise. Eventually Kirk is able to convince Dehner to act against Mitchell in an appeal to her remaining humanity. Of course Kirk is able to defeat them. Although she initially plays the role of a cold and distant scientist, she clearly falls in love with Mitchell and is also seduced by her new found abilities. In the end though, she knows that her duty is to her fellow humans and erstwhile crewmates.

Another excellent sci fi role for Kellerman was her second appearance on Outer Limits as Mrs. Judith Bellero, daughter of a wealthy CEO of a corporation working on modern weapons systems. Her husband, played by Martin Landau, is only interested in scientific achievement. An experimental device he is working on accidentally teleports an intelligent alien into his laboratory. He sees the opportunity to learn about a new civilization, whereas Judith sees this as an opportunity to exploit the alien by stealing his weapons technology and using it to promote her husband. The resulting drama develops like a Shakespearean drama and is very well played by all of the actors. Kellerman is particularly excellent as the tragic figure who eventually is trapped by the alien device and appears to go insane.