Baby still jerky movements at 3.5 months?

I know jittery or jerky movements are normal for newborns but anyone’s baby still do it at 3+ months?

Baby doesn’t do it all the time, but mainly only when laying back and usually playing or when excited. It’s almost like she’s shaking

Also sometimes she’ll stiffen her legs up while laying down (either after a kicking session or just randomly). Any other babies do this??