This study investigates the effects of background music-specifically, tempo and modeon consumer decision-making during utilitarian online shopping, using electroencephalography (EEG). To address the limitations of traditional self-report methods, which are often affected by social desirability bias, and to fill the gap in neuromarketing research within e-commerce, we conducted a controlled experiment with twelve healthy participants. Subjects performed a series of low- and high-complexity shopping tasks while recording EEG data. Twelve classical music excerpts, categorized into four non-lyrical tempo-mode conditions, served as auditory stimuli. We extracted band-power features from EEG to differentiate cognition states, complemented by repeatedmeasures ANOVA and post-hoc analyses. Results showed a significant effect of music condition on decision <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(F(13,11)=1.94, p=0.039)$</tex>, with fast-tempo minor-mode conditions significantly enhancing accuracy in low-complexity tasks compared to fast-tempo major-mode conditions <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(F(2,22)=9.91, p<0.001)$</tex>. However, mode differences were not significant under high-complexity scenarios <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(t(11)=0.29, p=0.777)$</tex>. EEG-based frontal alpha asymmetry revealed positive affective states in non-music, fast-major, fast-minor, and select slow-minor conditions, contrasting negative affect in most other scenarios. Interestingly, these neural affect indicators did not correlate strongly with decision accuracy or subjective valence ratings, suggesting music may have subconscious emotional effects independent of overt self-report measures.