"They’re friends," Johansson's rep tells PEOPLE of the pair, who joined another couple for the indie rock show at the Wiltern in Los Angeles. "They've worked together [on He's Just Not That Into You]. They’re not dating."
But they did seem to be having fun.
The two were described as being "flirty" in a "friendly" way during the evening. After the show, Johansson slipped backstage to hang out with the band's singer, Samuel Beam.
Another source reiterates that while Johansson, 26, is single ever since separating from her husband Ryan Reynolds, she has no romantic connection to Long.
"They're just friends," the source says. "They've known each other a long time."
Just last month, Johansson was spotted hanging out in Texas with Long's on-again, off-again girlfriend Drew Barrymore.
Reporting by ALEXIS CHIU, JENNIFER GARCIA and JESSICA HERNDON