"Members of Astro and fellow artists and staff at Fantagio are deeply saddened and shocked as we mourn him," the label said in a statement.
Mooonbin was a child actor before making his debut as a member of Astro in 2016. He was set to appear at a concert in the southern city of Busan next month as part of sub-unit Moonbin & Sanha.
Local media reported that the singer was found dead at his home in the Gangnam district of Seoul and that suicide was suspected. Police declined comment.
Suicide is among the leading causes of death for young people in South Korea. The country has the highest suicide rate among the OECD group of wealthy nations.
Following the news about the death of Moonbin, "all idols" trended on Twitter in South Korea.
"I hope all idols can chase their dreams without feeling heartbroken," read one tweet.
Moonbin’s death also became the most searched topic on China’s Twitter-like social media platform Weibo on Thursday morning, with many saying the news reminded them of the deaths of other young South Korean popstars in the past.
In 2017, Kim Jong-hyun, the lead singer of top South Korean boy band SHINee died in an apparent suicide aged 27.