No, Kava is completely legal, I never gotten any trouble from costums. Whatever you do make sure the Kava doesn't contain the leaves of the plant. Pacific Islanders have always discarded the leaves because they contain dangerous alkaloids. That's why a few people have had liver problems while on Kava.
I've bought it from a few different sites. My favorite is
www.kickbackwithkava.com, it comes in a powder form which I throw into some water. Have fun.