According to People, the pair were seen "flirting" at a birthday party in honour of R&B star Ray J in Los Angeles on Wednesday night.
A party guest said: "They never left each other's side. They were flirting all night and sipping from each other's drinks."
Patridge, 24, and Cabrera, 27, were also reportedly seen together at Sunday night's showing of Rock Of Ages on Broadway.
"[They] arrived together, and no one seemed to recognise them, they flew right under the radar," said an audience member. "They had drinks at their seat. They totally looked like a couple. It was really cute.
"They were holding hands and her hand was on his leg. They were very smiley with each other and joking around."
Patridge previously dated Hills co-star Justin Brescia, while Cabrera has been linked with Riley Keough and Ashlee Simpson-Wentz.