Authorities have locked down each of the five districts in the region, which borders China.
Two other people tested positive for the disease in the neighbouring province of Khovd, and a squirrel recently tested positive in the US state of Colorado.
While the latest news paints a grave picture as the world struggles to contain COVID-19, the Black Death hasn’t returned.
After its several global tours, the disease went on to form deadly pockets of endemic infection.
Nations such as China and Mongolia, some African countries and American states still find hundreds of cases per year.