Jin were diagnosed with COVID-19 on Saturday evening, the Big Hit Music agency said in a statement. It earlier said another member, Suga, tested positive for the virus on Friday.
All three took their second jabs in August, the agency said.
BTS is a seven-member boyband. The four other members are J-Hope, Jungkook, V and Jimin.
According to the agency, RM has exhibited no particular symptoms while Jin is showing mild symptoms including light fever and is undergoing self-treatment at home. The agency said Friday that Suga wasn't exhibiting symptoms and was administering self-care at home in accordance with the guidelines of the health authorities.
RM had tested negative after returning from the United States earlier this month following his personal schedule there. But he was later diagnosed with the virus ahead of his scheduled release from self-quarantine, the agency said.
After returning to South Korea this month, Jin underwent PCR tests twice — upon arrival and later before his release from self-quarantine — and tested negative both times. But he had flu-like symptoms on Saturday afternoon before he took another PCR test that came back positive, the agency said. Media reports said he also had traveled to the U.S.
Suga, who has had a number of personal engagements in the United States during the band's official time off, was diagnosed with COVID-19 during quarantine after returning from the U.S., the agency said.
The agency said it'll continue to provide support for the three members for their speedy recovery. It said it will cooperate with the requests and guidelines of the South Korean health authorities.
Since their debut in 2013, BTS has garnered global recognition for their self-produced music and activism, which includes giving a speech at the United Nations and publicly calling out anti-Asian racism.
BTS was named artist of the year and favorite pop duo or group, and also won the favorite pop song award for "Butter" at the American Music Awards in November.
In October, the group's collaboration with British rock band Coldplay, "My Universe," hit No. 1 on the Billboard Hot 100. It was BTS' sixth Hot 100 No. 1.