We have performed the first ab initio investigation of the boron compound BSb with zinc-blende structure, and have compared its structural and electronic properties with those of other boron compounds such as BN, BP, and BAs. The calculations are performed using a plane-wave expansion within the local density approximation and the pseudopotential approximation. Results are given for the lattice constant, bulk modulus, band structure, and total valence charge density. The electronic band structure of BSb proved to have features that differ from those of other III-V materials. It is found that BSb is less ionic than other III-V compounds, with an indirect band gap, and presents the same anomalous behaviour as BP and BAs.