Mayer, 36, turned up in Oxfordshire, England, where he gave an address at Oxford University's Student Union on October 25, reported E! online.
The singer looked dapper in khaki pants and a preppy cable knit sweater and shirt.
Many students in attendance took to Twitter to express their excitement about Mayer taking time out from his current British trek to talk to them.
"Studying at Oxford just became worth it after seeing John Mayer at the Union today! Amazing," tweeted incoming masters candidate Rebecca Miles.
Mayer was thrilled by the invitation. "Thank you to the Oxford Student Union for this afternoon. It was a great event," he tweeted.