The Hills star was reportedly seen flirting with Haynes at the HTC Status phone launch last week.
"She was into him, and vice versa. They went to a club afterward," a witness told Us Weekly.
However, an insider claimed that the two are nothing more than friends, saying: "They are friends and have known each other forever."
Haynes appeared on two episodes of The Hills in 2007.
Conrad split from boyfriend Kyle Howard in late June after three years of dating, but a source told the website that the two may reunite, noting that Conrad and Howard still speak to each other every day.
"They may get back together," said the source.
Conrad previously signed a three-book deal with HarperCollins, which will see the 25-year-old pen a trilogy titled The Fame Game.