<p>The metacognitive model of emotional disorders suggests that the cognitive attentional syndrome (CAS; i.e., a set of maladaptive self-regulation strategies) is activated by maladaptive metacognitive beliefs (i.e., beliefs about thinking). Positive and negative metacognitive beliefs are considered important for activating the CAS. Habitual use of CAS strategies is thought to exacerbate emotional distress, leading to the development of emotional disorders. To date, there has been limited longitudinal evidence (1) supporting the assertion that maladaptive metacognitive beliefs activate the CAS, which then leads to anxiety and (2) examining the distinct roles that negative and positive metacognitive beliefs play in CAS activation and anxiety. As such, the mediating role of the CAS in the relationships between positive and negative metacognitive beliefs and anxiety was examined using a cross-lagged design to make temporal inferences in the present study. Adult participants (<i>N</i> = 573) completed an online self-report battery at three time points across seven months. A series of path analyses showed that time 2 CAS activation mediated the relationship between time 1 negative metacognitive beliefs and time 3 anxiety. This effect was specific to negative metacognitive beliefs, as time 2 CAS activation did not mediate the relationship between time 1 positive metacognitive beliefs and time 3 anxiety.</p>