Why do i have small pus bumps in my arm? its not under my armpits just on arms.

Pus?: If truly pus, then you probably have a transient infection of the hair follicles called folliculitis. But if you're talking about small, hard bumps with a tiny amount of a waxy substance in them, especially on your upper arms and have chronic dry skin, then this might be the benign hyperkeratosis pilaris, which can respond to exfoliation and regularly using a good moisturizer.