John Mayer Will Guest Star on HQ Trivia Sunday -

John Mayer's taking his show on the road ... to make a special guest appearance on the popular live trivia game, HQ Trivia.

Sources close to the singer-songwriter tell TMZ ... he'll join host Scott Rogowsky -- aka Host Malone, aka Quiz Khalifa, aka Trap Trebek -- Sunday night to turn the daily game show into a wonderland ... with a prize of $25,000.

We're told John's set to queue up a question or 2 for all the HQties out there ... much like Robert De Niro did recently. Other celebs like The Rock and Jimmy Kimmel have guest hosted as well. We've learned John will also belt out a tune during the show's broadcast.

Make sure to have your phones handy and play with John and Scott Sunday night at 9/8c!!