Babies naturally explore everything in their world with their mouth - it's how they learn. It's completely normal for babies to chew on their toes, their toys, the table, lol - whatever is in their vicinity at that age they are going to try to put in their mouths to explore it. That's why baby proofing things is very important.
My advice, don't make a big deal about it and just distract your baby with something else fun and safe he can chew on. If you pay a lot of attention to it he may continue to do it to get your attention.