The neural mechanism underlying attentional bias in OCD (Obsessive-Compulsive Disorder) remains unclear. The goal of this study was to examine and compare the time course and the event related potential (ERP) components in OCD patients and healthy controls (HC) to reveal the complex brain activation pattern associated with attentional bias in OCD. The behavioural and electroencephalogram (EEG) data were recorded while the participants performed an emotional Stroop task. Compared to HC, the individuals with OCD exhibited slower response time, prolonged N1 latency and larger N1 and P2 amplitudes across different emotional words. In addition, we discovered that the OCD group showed an enlarged NI component to OCD-related threat words compared to neutral words. Moreover, the OCD group had decreased P3 and later positive potential (LPP) amplitudes towards all types of words compared to the HC group. More importantly, the OCD group manifested smaller LPP amplitude to threat words compared to the HC group. Our findings suggest that OCD individuals may excessively direct their attention away from the threat at the late processing stage, probably due to the intensive processing or overestimation of the stimuli in the early automatic processing stage.