It's always awkward when you're out to dinner with your fiancé and your ex-husband shows up -- but if you're "NCIS" star Pauley Perrette ... the cops get called.
Sources tell TMZ ... Perrette was at Shintaro Tuesday night -- a sushi joint in Hollywood -- when her ex-husband, Coyote Shivers, showed up ... and started snapping pics of her.
Problem is -- Pauley currently has a restraining order against the guy ... so when she saw him, the cops were called. But by the time police arrived, we're told Shivers had split.
According to our sources, cops are now investigating whether or not Shivers violated the restraining order that Perrette has against him.
Attempts to reach Coyote were unsuccessful.