any particular and persistent posturing in a child of any age may be abnormal and need to be evaluated.
few other questions i would like to ask would be about the birth history like whether the baby cried instantly, was there any antenatal infection you were having, was there any post natal infection or history of hospitalization in the baby, has he achieved the milestones normally etc.
any constant posturing with increased or decreased tone may be a sign of cerebral palsy
that may be caused by any perinatal insult. or may be without any known cause.
so you should get your child evaluated by a pediatrician
who would be in a better position to assess the child clinically and would be able to guide you better if anything needs to be done.
hope my answer guides you in right direction
thanks for the question,
Dr. Amit Kumar