We use density functional theory and the modified Becke-Johnson (mBJ) approach to analyze the electronic and magneto-optical properties of N-doped NaTaO3. The mBJ results show a half-metallic nature of NaTaO2N, in contrast to the generalized gradient approximation. We find a giant polar Kerr rotation of 2.16 degrees at 725 nm wave length (visible region), much higher than in other half-metallic perovskites and the prototypical half-metal PtMnSb. We explain the physical origin of this unexpected property. (C) 2012 Elsevier B.V. All rights reserved.