Is that normal? Or this may be a sign of autism?
No, it's not normal for an 8 month old child to have never smiled, ever. Infants smile spontaneously from birth (some people attribute this to intestinal gas. It's most likely a reflex.) But they begin to smile responsively between one to two months of age, and laugh at two to four months of age.
If you mean the baby doesn't smile for a camera, that's a completely different matter. I'll assume that's not what you mean. If the baby used to smile but doesn't anymore, and it's been this way for a few weeks, it's worrisome (but not necessarily only for autism.)
You ask about autism. With so entirely little to go on, no one can say. The best course of action is to bring this up with your baby's doctor. It is not too early to start doing testing on a baby who isn't reaching their milestones.