From Act 1 of Neil Simon's Last of the Red Hot Lovers:
Barney: As a matter of fact, it's my mother's apartment.
Elaine: You're not actively serious?

I've never heard 'actively' in this context. My instinct would be to say 'actually'. So, is this 60s-lingo, an
Americanism, a typo, or what? Any thoughts out there?