We caught up with Britney tonight at Romanov Russian restaurant in Studio City tonight -- but it appears NOT to have been just any dinner ...

A waiter at the restaurant told our photogs that Britney dined with Mel Gibson!

We're not sure why the two former Malibu Serra Retreat neighbors would meet up for dinner -- Is Mel casting for "The Passion of the Christ, Part 2?" Were they discussing his film "Paparazzi?"

Or maybe Gibson's on a mission to save Brit. He was quoted, in December 2006, as having some kind words for Brit -- Read the quotation, after the jump ...