Musical expertise has been shown to induce widespread structural and functional alterations in the brain, even-handedly affecting top-down and bottom-up factors. At the same time, it is known that the early evoked gamma-band response (GBR) can be modulated by top-down as well as bottom-up factors such as attention and sound intensity. In this study, we examined the effects of musicianship and attention on the intensity modulation of the auditory-evoked GBR. We compared the electroencephalogram of 17 professional musicians with that of 17 musical laymen obtained during either a forced-choice discrimination task (active) or a passive listening condition. Pure 1000 Hz sine tones were presented at three systematically varied sound intensities (40, 60, and 80 dB sound pressure levels). The results of auditory-evoked potentials and evoked GBRs obtained in the active condition predominantly corresponded to the findings of previous studies. Besides the already known augmentation of the early evoked GBR because of enhanced intertrial phase coherence with increasing sound intensity, we also observed stronger GBRs and enhanced phase locking under the active condition compared with passive listening, whereas the general shape of intensity modulation was comparable between the two conditions. In addition, phase locking to stimulus onset was increased for stimuli of all three intensities when attended, whereas in musicians, only stimuli of the highest intensity (80 dB) induced significantly increased phase locking under the active condition. Taken together, our results suggest that musical expertise influences attention effects on the intensity-modulated early auditory-evoked GBR with respect to intertrial phase coherence.