We recorded event-related potentials (ERPs) in 15 subjects in order to elicit a N270 of arithmetic conflict. Subjects calculated an arithmetic problem and matched their calculation result to an answer digit. They pressed a button when the presented digit is a true answer (condition 1) and pressed another button when the answer is false (condition 2). ERP components of P90, N130, P180, N200 and late positive component (LPC) were recorded in condition 1. In condition 2, N270 was elicited between N200 and LPC and it peaked at approximately 270 ms (268.6 +/- 29.0 ms at Cz). The peak latency of LPC in condition 2 (405.7 +/- 51.3 ms) is significantly delayed than condition 1 (307.5 +/- 22.7 ms). N270 reflects the endogenous conflict processing in human brain.