I'm looking for the first show that repeatedly placed a human on screen in the role of a mechanical man/woman that looks like a regular person without obvious "I'm a robot" make up. Secret robot access panels like the ones we see on Commander Data are OK.
There was a short-lived comedy (1964-1965, 26 episodes) called My Living Doll. Starred Robert Cummings and Julie Newmar. Julie played the character Rhoda Miller, a lifelike android.
From the IMDB page -
Rhoda is an extremely sexy young woman living with womanizing Air Force shrink Bob McDonald. What Bob knows and the rest of the world does not is that Rhoda's real name is AF 709, and she is actually a sophisticated (yet naive) robot. Bob's job is to teach Rhoda how to be a "perfect" woman, and keep her identity secret from the world -- especially lecherous neighbor Peter. When actor Bob Cummings left the series in early 1965, his character was written out of the series, and Peter was given the duty of taking care of Rhoda.
The only thing that comes to mind is the Get Smart TV show (1965-1970) which had Hymie the Robot:
Hymie the Robot (Richard "Dick" Gautier) is a humanoid robot built by Dr. Ratton to serve KAOS, but in his first mission, Smart manages to turn him to the side of CONTROL.
Hymie has numerous superhuman abilities, such as being physically stronger and faster than any human and being able to swallow poisons and register their name, type, and quantity, though his design does not include superhuman mental processing, most significantly characterized by an overly literal interpretation of commands.
For example, when Smart tells Hymie to "get a hold of yourself," he grasps each arm with the other. Hymie also has emotions and is "programmed for neatness."
Over the next three years, Hymie increasingly discovers his humanity.
Hymie looks completely normal but has a massive amount of wires/circuitry under his shirt.
My favorite Hymie moment was when Max says, "Kill the light" and Hymie shoots the light with a silencer.
Well Rosie, the maid from The Jetsons first appeared in 1962.
I would say she qualifies as the first mechanical robot regular on a television series, especially as The Jetsons originally aired in PRIMETIME.
Though Andromeda from the UK series A for Andromeda (1961) was a robot, though a biological robot. She was built in a lab by humans and designed by an alien super-computer.
I'm going to guess Future Cop. It first aired in 1976 and featured a police officer being partnered with a human-like experimental android.