Although the recognition of facial expressions seems automatic and effortless, discrimination of expressions can still be error prone. Common errors are often due to visual similarities between some expressions (e.g., fear and surprise). However, little is known about the neural mechanisms underlying such a confusion effect. To address this question, we recorded the magnetoencephalography (MEG) while participants judged facial expressions that were either easily confused with or easily distinguished from other expressions. The results showed that the fusiform face area (FFA), rather than the posterior superior temporal sulcus (pSTS), played a preponderant role in discriminating confusable facial expressions. No difference between high confusion and low confusion conditions was observed on the M170 component in either the FFA or the pSTS, whilst a difference between two conditions started to emerge in the late positive potential (LPP), with the low confusion condition eliciting a larger LPP amplitude in the FFA. In addition, the power of delta was stronger in the time window of LPP component. This confusion effect was reflected in the FFA, which might be associated with the perceptual-to-conceptual shift.