The chapters describing the simplification performed by Maxima requires some basic calculus understanding, such as differentiation and integration. But the focus is on the programming techniques, not on math, so it doesn't get too deep. It's more important to think logically, rather than having a deep or broad mathematical background.
Thanks. I'll work through Calculus too. Hope high-school Calculus (1, 2, & 3) should be good enough!