It's a Mystery, Charlie Brown
- taona: 1974
- Firenena: United States of America
- Genre: Animation, Comedy
- Studio: Lee Mendelson Film Productions, Bill Melendez Productions
- Keyword: detective, dog, beagle
- tale: Phil Roman
- Cast: Todd Barbee, Melanie Kohn, Stephen Shea, Donna Le Tourneau, Jimmy Ahrens, Lynn Mortensen