According to the site, Yoshida, 25, received a polymerase chain reaction (PCR) test on January 7 in preparation for a theater performance two days later.
The positive result was confirmed on January 8. Two staff members for the group were deemed close contacts, the site said.
Yoshida does not have any symptoms of COVID-19, which is the disease caused by the coronavirus. She is now staying at home, the site said.
“Going forward, we will use instructions from medical institutions and health centers while continuing to devote ourselves to her recovery,” the agency said. “We will take further measures to ensure the safety of our members, fans and staff while also preventing the spread of infection.”