Aniston and Mayer birthday bash

Jennifer Aniston helps John Mayer celebrate 31st birthday

Jennifer Aniston is doing nothing to diffuse the rumours that she's back on with John Mayer after helping the singer celebrate his 31st birthday on Wednesday night.

In their third outing together in a week, the pair headed to the members-only Grand Havana Room in LA, after stopping in at a party for Jen's pal David Arquette's new clothing line, Propr.

One onlooker told People magazine: 'They seemed to be having a great time.

'They were sitting next to each other. They're a very good-looking couple and seemed happy together.'

The night before, the on-off couple enjoyed dinner with three friends at the Sunset Tower Hotel, just days after they were spotted dining in Boston and New York over the weekend.

The pair were seen taking in a Ray Montagne concert in Boston on 10 October and again on Saturday, when they enjoyed a romantic dinner at Il Mulino in New York.

America's National Enquirer reported that the two flew from New York to Los Angeles together on Sunday night after frequently seeing each other over the weekend.

Whatever's going on, it's great to see a smile on Jen's face again...

JENNIFER ANISTON PHOTOS