The body of Koo Hara, 28, was discovered at her home in southern Seoul, Yonhap said. Police were not immediately available for comment.
Koo, better known as Hara in other parts of Asia, had spoken out against cyber bullying. In June, a month after she was found unconscious at her home and hospitalised, she said it was difficult to overcome depression and pleaded for positive comment on social media.
She debuted with the five-member Kara in 2008. It was one of the early girl groups that helped fan the global K-pop wave, building large fan bases in Japan, China and other countries.
After a deal with a South Korean management agency was terminated, Koo launched a career as a solo artist in Japan and held a concert there this month.
Another K-pop star, Sulli, a former member of girl group f(x), who was a close friend of Koo’s and had also spoken out against cyber bullying, also died in October.