Creative idea generation plays an important role in design process. Our study aimed to use physiological signals to evaluate the effect of music on idea generation in individual and group conditions. Thirty graduate students with design experience were recruited to generate ideas for specific design topics and sketch these ideas. The experiment included a total of six trials of design tasks under three kinds of music conditions (positive music, negative music, and nonmusic) and individual/group conditions. Electrocardiography (ECG) and electroencephalography (EEG) data were collected for objective evaluation; the quantity and quality of design ideas were recorded and rated for subjective evaluation. The results showed that participants produced more ideas in positive music condition, but the quality of the design ideas was worse; group condition was more likely to evoke pleasant emotions. We also found that heart rate fluctuated in different music and individual/group conditions; alpha2 activity was closely related to creative idea generation, and theta activity was affected by different music conditions. These findings demonstrated that positive music was useful when more ideas were needed in the early stage of design process, and nonmusic was a better choice for a stage requiring deeper thought. Our study reveals the effect of music on idea generation, and helps to explore the influence mechanisms of emotion and brain neural activities of cognitive process in our daily work.