The cytochrome P411 enzyme is a variant of cytochrome P450_BM3 from Bacillus megaterium whose active site is an iron porphyrin imine ([Fe(Por)(NH)]^-) specie. This specie has been reported to successfully promote the primary amination of benzylic and allylic C(sp³)−H bonds. We employed density functional theory to study the electronic structure of the active site of P411 enzyme and the primary amination of C−H bond reaction that it catalyzes. The calculated spin densities and orbital values indicate the existence of resonance in this specie; namely, [(por)(–OH)Fe^IV–N^2-–H]^- ↔ [(por)(–OH)Fe^III–N^•-–H]^-. The amination of C(sp³)−H bonds consists of two main reaction steps: hydrogen-atom abstraction and radical recombination, and the former is demonstrated to be the rate-determining step. Furthermore, we studied the regioselectivity of the amination of primary and secondary C(sp³)−H bonds. Our calculations indicated that the secondary C(sp³)−H bonds of the substrate would be more favored for the activation by P411 enzyme. These results provide valuable information for understanding the properties and selectivity of C−H/C−N bond-activation reactions catalyzed by the P411 enzyme or other similar enzymes.