AceShowbiz -

Rihanna and Rob Kardashian enjoyed a weekend together to celebrate a friend's birthday. The Bajan singer and the reality TV star went to Racer's Edge Indoor Karting in Burbank, California for go-kart race and later hit Playhouse nightclub in Hollywood for a night of partying.

Riri and Rob were joined by a couple of friends including her stylist friend Mariel Haenn. Riri finished first while Mariel was the runner-up. The latter tweeted a picture from the August 25 outing and jokingly wrote, "2nd place on the left. 1st place on the right. She cheated."

Riri wore an oversized varsity jacket, shorts and converses, while Rob donned a gray vest, brown pants and Nike trainers. She later traded her sneakers with a pair of black thigh-high boots. At one point, an annoyed-looking Riri was seen giving a middle-finger salute to the paparazzi.

There's no word on whether Riri and Rob were dating, but Rob was romantically linked to her singer friend Rita Ora after he tweeted fake tattoos of each other's names on their hands, "S*** got crazy tonight... What can I say... #tatmynameonya."

Riri's ex Chris Brown reportedly was also at the club on the Saturday night, but he didn't join her group. Rita was not among the group either as she's busy promoting her debut album in the United Kingdom.