This is something I've heard in some TV show. I don't remember which one. I just wrote it down when I heard it.

Here it is.
-I'm on protecting the public.
-Are you still on saving your girlfriend?

What I'm especially interested is the meaning of on in these sentences. What does it mean or imply?

This is something I've heard in some TV show. I don't remember which one. I just wrote it down when I heard it.

Here it is.

-I'm on protecting the public.
-Are you still on saving your girlfriend?

What I'm especially interested is the meaning of on in these sentences. What does it mean or imply?