The "As Long As You Love Me" hitmaker was spotted offering acting tips to the "17 Again" star, 28, when they partied at Efron's home earlier this week, reported Us magazine.
"(Justin told Zac) to be more selective about the roles he takes. Justin was very honest and kind of went in on Zac but Zac appreciated it.
"Zac told Justin to keep breaking boundaries. He was giving him life tips," a source said.
The 22-year-old singer has also been giving Kylie Jenner advice on how to cope with fame at a young age.