Baby seizures? Help

My baby is 6 months old. And I’ve noticed a few times when I hold her it seems like her body shakes almost like it was vibrating but she’s just sitting there calm. When it has happened she’s sitting facing away from me so I’ve never seen her face while it happens. But today when putting her down for a nap, when I laid her down one of her arms just started vibrating like crazy, lasted a few seconds and then stopped. I’ve mentioned it to her pediatrician and she just said baby’s make weird movements sometimes. But her dad did have seizures as a baby. Does anyone else’s baby do this?