Ferromagnetic hexagonal α-MnAs has a first-order phase transition to β-MnAs at about 40°C. Because it shows no long-range antiferromagnetic order, most workers assume that it is paramagnetic in spite of the fact that it does not have a Curie-Weiss magnetic susceptibility. With the aid of density functional calculations, we show that it is antiferromagnetic and explain the lack of observed long-range order.