The purpose of this study was to determine whether frontal midline theta activity (Fmθ), an indicator of top-down sustained attention, can be used to distinguish an individual's best and worst golf putting performances during the pre-putt period. Eighteen golfers were recruited and asked to perform 100 putts in a self-paced simulated putting task. We then compared the Fmθ power of each individual's 15 best and worst putts. The results indicated that theta power in the frontal brain region significantly increased in both best and worst putts, compared with other midline regions. Moreover, the Fmθ power significantly decreased for the best putts compared with the worst putts. These findings suggest that Fmθ is a manifestation of sustained attention during a skilled performance and that optimal attentional engagement, as characterized by a lower Fmθ power, is beneficial for successful skilled performance rather than a higher Fmθ power reflecting excessive attentional control.