Mel Gibson was snapped in the middle of some PDA with a babe in Rome … but TMZ has learned he’s back in the U.S. — and very single — having just wrapped on a massive project.

Here’s the deal … the actor-director star and the Italian celeb Antonella Salvucci were snapped smooching in Rome … which, of course, led fans to ask “What’s going on, Romeo?”

Sources with knowledge tell TMZ … the pictures were of Mel saying goodbye to a good friend … he’s single and has been back in the U.S. for about a month, having just wrapped “The Resurrection of the Christ: Part One” — the follow-up to his 2004 blockbuster “The Passion of the Christ.”

As we reported … Mel and longtime partner Rosalind Rossseparated last year … after nine years and one child together. And those pics with Antonella were the first of Mel and a possible new squeeze — so, a big deal.