Police said an acquaintance found the 28-year-old dead at her home in southern Seoul and reported it to authorities.
The cause of death wasn't immediately known. Police refused to provide further details.
Goo made her debut in 2008 as a member of the girl group Kara, which had big followings in South Korea, Japan and other Asian countries. She later worked as a solo artist and appeared on many TV shows.
In May, Goo was reportedly found unconscious at her home and was hospitalized.
She was embroiled last year in public disputes with an ex-boyfriend who claimed to be assaulted by her. Goo accused the man of having threatened to circulate a sex video of her. The case made her the subject of tabloid fodder and malicious online messages.
In October, another K-pop star and actress, Sulli, was found dead at her home near Seoul.
The 25-year-old was known for her feminist voice and outspokenness that was rare among female entertainers in deeply conservative South Korea. Before her death, she appeared in a TV show and spoke out against online backlash she received over her lifestyle.