In this work we study relative stability, structural and electronic properties of pure BN and with substitutions of carbon by boron and nitrogen atoms, e.i. for B0.9375C0.0625N and BC0.0625N0.9375, respectively. Using first-principles calculations in the Density Functional Theory (DFT), we found that it is more energetically favourable that the carbon atoms occupy the positions of the boron atoms (C by B). It was found that the new compounds BC0.0625N0.9375 (C by N) and B0.9375C0.0625N (C by B) have high bulk modulus, so they are very rigid. This property makes them good candidates for applications in hard coatings or devices for high power and temperatures. The density of state calculations shows that compound has metallic behaviour due to the hybridization of the orbitals C-2p and N-2p that cross the Fermi level.