The aim of the study was to investigate mathematics anxiety in autistic school-aged boys compared with non-autistic peers, by considering the distinction between trait and state components of mathematics anxiety. The study involved 110 boys aged between 8 and 16 years old: 50 autistic participants without intellectual disability and 60 non-autistic peers. The two groups were matched for age and full-scale intelligence quotient. Trait mathematics anxiety was assessed with a self-report measure, whereas state components of mathematics anxiety were measured in the context of a real-time assessment, in which participants had to report their emotional (valence, arousal) and cognitive (perception of competence, worries) responses before and after completing a math task with time pressure. Findings revealed no significant group differences for trait mathematics anxiety. However, autistic participants performed worse in the timed math test than non-autistic peers. After controlling for age and trait mathematics anxiety, lower valence, higher pre-test emotional arousal, and higher worries were reported by the autistic boys compared with the non-autistic counterparts. No group differences emerged for perception of competence. This study emphasizes the importance of considering the distinction between trait and state mathematics anxiety, in addition to acknowledging the impact that emotional aspects, thoughts, and worries may have on the school experience of autistic students.