The incident took place one day before the lunar calendar's first anniversary of the death of Unification Church founder the Rev. Sun Myung Moon, but the motive was not immediately clear.
Gapyeong fire official Kim Oh-Jeong said a 53-year-old woman set herself, a 54-year-old man and a 57-year-old woman on fire inside the lobby of CheongShim Village, a retirement community operated by the Unification Church northeast of Seoul. South Korean news agency Yonhap said the three are church followers.
Kim said they suffered second- and third-degree burns that were not life-threatening.
Yonhap said police were investigating the motive but had ruled out religious reasons. It said the 53-year-old woman had shown symptoms of depression.
The man she set on fire was a pastor who was traveling with her, Yonhap said, adding that they were in the lobby to check in at the retirement community.
Unification Church spokesman Ahm Ho-yeul said he was not aware of the incident. Police officials investigating the incident could not be reached for comment.