Background: The brain mechanisms that underlie the psychological effects of auditory stimuli during physical activity are hitherto under-researched; particularly so in ecologically valid settings. The objective of the present experiment was to investigate the effects of two contrasting auditory stimuli conditions on psychological responses and brain activity during an outdoor walking task. Methods: Twenty-four participants were required to walk 400 m at a pace of their choosing and report perceptual (state attention and perceived exertion) and affective (valence, arousal, and perceived enjoyment) outcomes immediately after each exercise bout. Three conditions were administered in a randomised and fully counterbalanced order (control, podcast, and music). State-of-the-art, portable EEG technology was used to facilitate measurement during the walking task. Fast Fourier Transform was used to decompose the brain's electrical 40 activity into different band waves (lower-alpha, upper-alpha, sensorimotor rhythm, and beta). Results: The results indicated that music up-regulated beta waves, led to more dissociative 42 thoughts, induced more positive affective responses, up-regulated arousal, and enhanced 43 perceived enjoyment to a greater degree when compared to control and podcast. 44 Conclusions: Rearrangement of beta frequencies in the brain appears to elicit a more positive 45 emotional state wherein participants are more likely to dissociate from internal sensory 46 signals and focus on task-irrelevant factors. The portable EEG system used in the present 47 study appears to accurately measure electrical activity in the brain during light-intensity 48 physical activities and is effective in reducing electrical artefacts caused by body and cable 49 movements. 50