Spin properties of charge carriers photoexcited in the P3HT:PC₆₁BM and PCDTBT:PC₆₁BM composites were studied at X-band EPR spectroscopy. Light-induced EPR spectra were deconvoluted and the contributions of all spin charge carriers were determined. The main magnetic resonance parameters of charge carriers obtained were compared with those determined at millimeter EPR wavebands and analyzed as a function of electron precession frequency. The linewidth of spin charge carriers was established to originated mainly due to the weak anisotropy of their g-factors. The external magnetic field significantly affects dynamics, electron relaxation and recombination of spin charge carriers.