Is it normal that my baby is not yet rolling over?

Depends. Depends on how old your baby is babies start to roll over around 3-4 months depending on the baby. Discuss with your baby's doctor if you are concerned.
Yes. If your baby has not been on their belly much and are very comfortable on their back at all times they may not be inclined to roll. Babies are not expected to roll very early but some have rolled at their first doctor visit! If your baby is not improving in their head lifting or arm strength with repeated belly positioning over the first month or two, it is important tell your doctor.