One of the psychological states that can be monitored and influenced during learning in order to improve its various aspects is the state of anxiety, and one possible index of this state is frontal EEG beta. However, frontal EEG beta has also been associated with mental activities. This may imply that frontal EEG beta would not be a reliable index of anxiety in situations, such as learning, where significant mental activities can be involved. The present study investigated the relationship between frontal EEG beta and anxiety during computer-based learning. The frontal EEG beta and anxiety levels of four groups of 15 students were measured during learning conditions that comprised any of combinations of anxiety reduction and mental activities, anxiety reduction alone, or no treatment. The groups that combined anxiety reduction with mental activities showed significant increase in frontal EEG beta even though they recorded significant reduction in subjective anxiety. This may suggest that frontal EEG beta is not a reliable index of anxiety during computer-based learning.