The 36-year-old Cruel Intentions star reportedly had a three-month relationship with actress Amanda Seyfried last year, but has now been romantically linked to the S&M singer.
The pair are said to have “hooked up” several times over the last few months.
A source told US magazine Us Weekly: 'They initially hooked up when things were strained with [Rihanna's ex-boyfriend] Matt Kemp.'
The two met again at Bing's Two Kings charity event this month and celebrated Rihanna’s 23rd birthday together at a party in Beverly Hills this week.
A source added: 'They hung out a bit, but were discreet.'