The I Kissed A Girl singer, 27, played it low-key wearing an olive green jacket, black beanie, a floral scarf and glasses while John, 35, wore a blue jacket and black pants on the outing to the Japanese restaurant.
The two have been joined at the hip since taking their relationship public over the past few months.
They spent Christmas together, with Katy tweeting an image of John dressed up as Santa.
As we previously reported, Katy, since her marriage to Russell Brand, briefly dated Florence + The Machine guitarist Robert Ackroyd before hooking up with Mayer, who's dated Minka Kelly, Taylor Swift, Jennifer Aniston and Jessica Simpson, among others.
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