People with autism spectrum disorder (ASD) exhibit comorbidity with anxiety. The aim of this study was the investigation of the perception of teachers on anxiety in school children with ASD. The Scale Teacher Response (SAS-TR) questionnaire was completed by 291 special education and 118 general education teachers, providing data on students in their classes with ASD and of typical development (TD), respectively. According to the total scores on SAS-TR, 46.8% of the children with ASD presented levels of anxiety within the clinical spectrum compared with 15.3% of the children of TD. Gender and age were not associated with the anxiety scores, but in the children with ASD, higher intelligence quotient (IQ) was weakly, and better verbal skills more strongly correlated with a higher anxiety level. Teachers' awareness of anxiety symptoms in children with ASD may contribute to their social inclusion.