In reading, eye movements are typically influenced by both higher-level and lower-level cognitive processes that are affected by individual differences such as working memory capacity. However, the extent to which working memory impacts reading under increasing task demands remains uncertain. Therefore, this study aimed to explore the influence of working memory capacity, assessed via the n-back task, on peak saccade velocity during reading when an additional memory task is introduced. Thirty-one healthy participants with normal or corrected-to-normal vision read sentences performing either comprehension task or dual task on comprehension and working memory span. The results of the comprehension task were used as a baseline to track the differences in eye movement measures in the dual task with the increasing task demand. Participants who performed well in the n-back task exhibited higher peak saccade velocity during both single and dual reading tasks, particularly as the task demands increased: reading for comprehension while simultaneously maintaining six items in working memory was associated with the highest peak saccade velocity. Conversely, those with n-back lower performance did not display significant changes in peak saccade velocity. This discrepancy is attributed to task-induced variations in arousal among high-performing individuals. The study underscores the importance of individual differences in working memory and suggests a potential link between arousal and cognitive processes involved in reading comprehension.