The results of electrically detected magnetic resonance (EDMR) experiments on organic Schottky barrier diode based on regioregular poly(3-hexylthiophene-2,5-diyl) [P3HT] are presented. The existence of positively charged trapped polarons and bipolaron formation process with mobile polarons of the same kind are responsible for the EDMR signal. Variable frequency EDMR measurements indicate that spin-orbit coupling effects on the EDMR linewidth.