The 'Can't Be Tamed' singer was spotted leaving a Hollywood recording studio within minutes of Bieber, 19, and they are believed to be working on a collaboration, reported E! online.
"There aren't that many recording booths at this studio, they must be doing something together. Justin and Miley left within minutes of each other - it's too coincidental. There's gotta be a collaboration in the works," a source said.
Cyrus recently worked with gangster-rapper-turned-reggae artist Snoop Lion on the song 'Ashtrays and Heartbreaks'.
"Miley Cyrus was always a great singer to me and I knew she was a fan so it was great for us to collaborate. It's what she's going through and what I'm going through, she makes great music," a source said.