The confirmed case has meant that some pupils and staff at Llanidloes High School have been asked to self-isolate after a pupil tested positive for Covid-19.
Families of pupils that have been identified as having had potential contact with the case have been informed of the situation.
Cllr Phyl Davies, Cabinet Member for Education, said: “Our education officers have worked quickly with staff at Llanidloes High School to minimise the risk for everybody concerned. Affected families have been contacted by staff.
A focussed clean has taken place at the school and all other pupils will continue to attend school next week as planned.