The Attention Network Test (ANT) is a well-established paradigm for assessing the three attention systems of the Posnerian model: alerting, orienting, and executive networks. Yet most studies have failed to elicit mental fatigue in the form of objective performance deterioration, even when using prolonged ANT versions. This study examined a modified ANT to induce fatigue and explored the differential effects of fatigue on the three systems. Eleven healthy adults completed personality and impulsivity questionnaires and reported on their current mental (e.g. state anxiety and depressive symptoms) and physical state before performing a 45-minute ANT. The protocol successfully induced both subjective and objective fatigue, as reflected in increased visual-analogue fatigue ratings and performance decline in the form of reaction time increases. Although the three attention systems showed different tendencies throughout the task, they did not appear to be affected differently by time on task, as reaction times increased similarly across trial types. However, it is plausible that individual differences underlie this pattern, as the fatigue sensitivity of the respective systems depended on cognitive, affective and personality variables. Specifically, the decline in executive attention over time correlated negatively with depressive symptoms and positively with cognitive impulsivity and attention-deficit scores. Deterioration in the orienting network correlated negatively with impatience. These findings suggest that the effects of mental fatigue are more generalized across the systems, rather than exerting their influence through a single system. However, the systems show individual differences, and exhibit distinct cognitive and affective correlates.