Autism spectrum disorder (ASD) is a severe neurodevelopment disorder. This study tests the hypothesis that children with ASD show atypical intrinsic complexity of brain activity. Electroencephalogram data were collected from boys with ASD and matching normal typically developing children while performing an observation and an imitation task. The multiscale entropy was estimated within the 0.5-30 Hz frequency band over 30 time scales using a coarse-grained procedure. A decreased electroencephalogram complexity was observed in the ASD children both during the observation and during the imitation tasks. On comparing the two tasks, significant differences were observed between groups in the right hemisphere, and also the central cortex for the observation task. Multiscale entropy could provide further evidence of the relationship between ASD and cerebral dysfunction.