The case was a student who had been repatriated from the Philippines earlier in the week.
He tested positive upon arrival, despite passing three earlier tests before departure while awaiting his flight.
The student, who was asymptomatic, was now in isolation with two other close contacts.
Front-line staff were also being assessed.
When announcing the case, Prime Minister Manasseh Sogavare said the preparedness and response measures the government had worked on implementing over the past eight months had now been activated.