While practicing emotional design, usually experts suggest that the surprising and contradiction is a prelude to evoke users' positive emotion associated with humor. In this study, the scientific experiments were implemented to examine the event-related potential (ERP) brainwave signal as well as "incongruity" condition. The analysis was carried out to the specific ERP components - N270 and N400. N270 is an endogenous ERP component of conflict effect; the N400 associated with the emotion of confusion. This experiment presented the stimuli with the combination of coherent/contradiction conditions and humor/neutral attributes, and recorded the ERP signal to detect brainwave variations. By analyzing these two components at medial part scalp sites - Fz, Cz, and Pz, the result evidenced that the humor products with contradiction condition did evoke greater brainwave amplitude, and correspond to the experts' design guidelines.