The couple - who announced their split last week after dating for almost two years - have fuelled speculation of a reconciliation after Justin picked up Selena at Los Angeles International airport before they stayed at her home overnight, according to gossip website TMZ.
On Thursday they were also spotted together at the Four Seasons Hotel in Beverly Hills.
Selena, 20, and 18-year-old Justin were believed to have held crisis talks in New York last weekend to discuss where their relationship was going after their split was confirmed.
A source said: ''I saw Selena go into her hotel in New York around 17:40 and not even three hours later, Justin went in. I saw him leave around 23:00.
''It's not just over for Justin and Selena, whatever happens they have a lot to talk about.
''They're both being a bit cagey and stubborn but they're desperate to see one another. This isn't new for them; they often have a tumultuous relationship. We all expect them to work it out.''