The purpose of this study was to explore how different transaction risk scenarios on auction platforms can significantly and differently influence online consumers’ brainwaves. In this study, four scenarios (a 2 × 2 experimental design, i.e., one-two transaction products and with-without transaction labels) were developed. Twenty male participants (from engineering and liberal arts programs) assigned to view all four scenarios were recruited. In each scenario, the participants must determine whether they should make a transaction for purchasing products as accurately and quickly as possible. By using a 40-channel digital EEG amplifier with a cap, the participants’ purchasing decision-making responses were recorded and timed, and their brainwave data were detected and stored for data analysis afterwards. After the experiment, every participant received an appreciation reward worth about $10 USD. All the brainwave data were analyzed using the software SCAN 4.5. As a result, it was found that participants spent more time and were less accurate without textual transaction labels than with the labels regardless of purchasing one or two items. Specifically, the participants’ decision-making response efficiency and accuracy rate performed the worst in the scenario which did not offer any feedback for determining two transaction items. Also, when comparing the with-without textual feedback scenarios, the participants’ brainwaves were found to be different.