Based on ab initio calculations for Fe-Al B2 phase with and without the vacancies, the authors studied the influence of alloying by Ni, Cr, and V on the energy of vacancy formation. The authors predict that the presence of these alloying elements in the vicinity of the vacancy on the Fe site increases the energy of the vacancy formation. The present article discusses the changes of the electron charge redistribution in the vicinity of the vacancy in Fe-Al alloyed with these transition metals and link the preference of their site occupation with the peculiarities of the electron density redistribution. In addition, the authors report on the results of calculations of different types of antisite defects in Fe-Al and show that the formation of the antisite on the Al site is the energetically preferable configuration for this defect. The obtained results are in agreement with the experimental data.