The two were seen being "very cuddly" with one another during Coldplay's LA concert on Wednesday, an eyewitness told E! News.
Following the show, Bosworth and Polish made no attempt to "cover their faces" and were snapped by several photographers, the insider added.
Reps for both stars haven't yet commented on whether they are dating.
Bosworth reportedly split from her Straw Dogs co-star Alexander Skarsgård earlier this year.
Polish and Bosworth's film Big Sur, which is based on Jack Kerouac's 1962 novel, is expected to be released in 2012.
Watch Kate Bosworth in the trailer for Straw Dogs, opening September 16 in the US and on October 28 in the UK, below: