EXCLUSIVE

Jamie Luner -- you know her as Lexi Sterling on "Melrose Place" -- has been accused of sexual misconduct with an underage male ... TMZ has learned.

Law enforcement sources tell TMZ ... a man in his 30s filed a police report with the LAPD alleging that back in 1998 Jamie performed oral sex on him when he was just 16.

The nature of the relationship is unclear -- whether the man was a teen actor or just someone she knew. Cops are investigating like they would anyone who reports a crime, but their hands might be tied ... with the statute of limitations in California having lapsed.