Should I be concerned if my baby boy who is almost 4 1/2 months is not cooing or babbling?

I felt like he was cooing alot around the 2 month mark and now I rarely ever hear him cooing or babbling. Developmentally he seems to be right on target. He is holding his head up, rolling over, smiling and laughing etc... Any advice or comments. I of course am so concerned about Autism and he is my first so I am just very concerned.