A comparative study of the band structure and magnetic properties of the hexagonal and cubic modifications of aluminum nitride doped with boron, carbon, and oxygen in the nitrogen sublattice has been performed using the ab initio FLAPW-GGA method. Preliminary conclusions on the comparative chemical activity of these phases are drawn from estimates for the energies of substitution of nitrogen atoms by dopants. It has been shown that the doping with boron and nitrogen leads to transition of hexagonal AlN into a magnetic state with high spin polarization of near-Fermi electrons, but for cubic AlN, this effect is absent.