Pine, 36, and his "Star Trek Beyond" co-star enjoyed the NYLON Midnight Garden Party with Troian Bellisario and Patrick J Adams, reported E! Online.
According to a source, the duo came around midnight with a whole group and stayed at the party for about 90 minutes.
"They were super cute. Chris kept stepping back to let her have the spotlight and wouldn't take photos but kept watching her when she would pose.
"They were together the entire time and kept walking with his hand around her waist," the source said.