While behavioral issues are often associated with autism, they do not necessarily mean a child is autistic. It would probably be tough to find a kid out there who does not exhibit any type of behavioral problems at some point.
That said, the Autism Society states that early diagnosis is key to finding the right intervention approaches to help a child out. If a child is suspected of being autistic, it's best to contact his or her pediatrician, school psychologist, or a specialist in the area. Those professionals are equipped with the knowledge and resources to most effectively screen a child for autism.
I'm also including an article below that focuses on the diagnosis and consultation process. I hope it helps!