The two were spotted getting cozy together at an after party with Missy Elliott, who tweeted a pic of the happy trio.
A source also revealed to UsWeekly.com that Mayer was waiting behind the scenes to congratulate Katy when she came off stage.
Although the two officially split in February 2014, Perry and Mayer have sparked reunion rumors in recent weeks by being seen out and about in Los Angeles.
Perry's most recent fling, Diplo, sent his ex a congratulations message after her show-stopping halftime special. "@Katyperry murdered it.”