The 25-year-old pop singer said he had been "feeling super disconnected and weird".
In the message on Instagram, he told his 105 million followers: "Just wanted to keep you guys updated a little bit hopefully what I'm going through will resonate with you guys.
"Been struggling a lot.
"Just feeling super disconnected and weird.
"I always bounce back so I'm not worried just wanted to reach out and ask for your (sic) guys to pray for me."
Thousands of fans replied to praise his honesty and to offer support.
Last month it was reported in US media that Bieber was being treated for depression.
Bieber married model Hailey Baldwin last year and has also spent recent years rekindling his Christian faith, something he has talked about regularly in relation to his marriage.
In the Instagram post he added: "God is faithful and ur prayers really work thanks .. the most human season I've ever been in facing my stuff head on."
© Sky News 2019