No federal or state taxes removed from wal-mart paycheck?

So i ws looking at my next paystub online and for some reason they didnt take out any federal or state taxes. this is like my 4th paycheck and they have tooken out both of these every time. i recently had t do my W4 online for some reason and i filled it out the same way again. i put 0 exemptions and all that stuff just like i did when i started. so should i worry about this or what? cuz i dont want to have to pay taxes cuz of a mess up. thanks :)