The seven-member group is on temporary break while members carry out South Korea's mandatory military service.
South Korea has one of the world's largest active armies to defend against North Korea, with all able-bodied men between the ages of 18 and 28 required to serve between 18 and 21 months.
There has, however, been public debate over whether BTS members should be given exemptions considering their contributions to the lucrative K-pop industry.
The group's main rapper and leader RM and vocalist V will enlist on December 11, while Jimin and Jung Kook will follow suit the next day, Yonhap reported.
After initial training, the four will serve as active-duty army soldiers for 18 months, according to another report in entertainment media outlet Star News.
BTS' management agency HYBE, which has said the four had begun the process of enlistment, did not immediately respond to a request for comment.
Earlier this month, Jung Kook announced in a blog post he would serve in the military in December.
Jin, 30, the group's oldest member, is set to be discharged from military service in June.
