The X Factor boss and the True Blood beauty enjoyed a meal at Hollywood restaurant Cecconi's, according to reports. Photos show Simon, 53, and a smiling Janina, 32, being driven away together after their dinner date.
The night out followed some online flirting between the pair.
Last month Simon tweeted the actress, writing: "Hello trouble."
The brunette replied "... who me??" with the hashtag #DefinitelyMe, and Simon answered: "Yes you."
It's the latest speculation about a romance for Simon, as earlier this year he was linked to F1 driver Jenson Button's former fiancee Louise Griffiths.
He was also seen on a dinner date with former Baywatch actress Carmen Electra earlier this year and last month there were rumours he had rekindled his romance with his ex-fiancee Mezhgan Hussainy after the pair were snapped during a day out in Beverly Hills.