My baby likes to make his head bump on things. Will it affect his mental development?

Take your child to.. Your child is less likely to get hurt. The more important question is why it happens. This is the root problem that must be dealt with!
Pattern behaviors. This is often a transient pattern of self stimulation.They do not hit their head hard enough to do damage.It is often adopted as a form of self soothing that will change as they transition to other behaviors. I consider it similar to thumb sucking, with more flare.