E.T.
I think your son is exhibiting normal jealousy of his sibling. My daughter did more of this a few months ago, but my son is 1.5 months older than your baby boy.
I have found it helpful to emphasize to my daughter that she is a BIG sister and enlist her in helping with her brother. It isn't a perfect cure for jealousy, but it helps a lot. Further, I remind her that her brother is a baby and that she is a big girl.