The authors determine the bulk and surface canted-paramagnetic phase boundary of uniaxial antiferromagnets as a function of temperature for a semi-infinite system. Within the Green-function formalism, they show that the canted-paramagnetic critical field at the surface, which depends on the ratio the surface to bulk exchange coupling, is larger than that corresponding to the bulk. This critical field at the surface does not follow a T^3/2 Bloch law, but instead decreases linearly with temperature. At a given temperature, which also depends on the ratio of the surface to bulk exchange coupling, the surface critical field becomes identical to that of the bulk.