Mind wandering (MW) involves a shift of attention from external tasks to internally generated thoughts, but its relationship with executive functioning remains unclear. This study examined whether MW is associated with set-shifting performance in the Number–Letter Task (NLT) and whether this relationship is moderated by non-executive task difficulty, measured using a Random Dot Motion (RDM) task. Forty-one participants completed both tasks across five sessions with embedded experience-sampling probes to assess attentional state. Performance was analyzed using generalized linear mixed-effects models.MW was associated with reduced accuracy across tasks, indicating a general performance cost during off-task states. Task difficulty also impaired performance, with lower accuracy on harder trials. However, MW did not differentially affect performance across trial types, and no significant interaction between attentional state and difficulty was found. A marginal three-way interaction suggested that MW effects may vary across task types and difficulty levels. Overall, findings suggest that MW reflects general attentional disengagement rather than a specific impairment in executive control.