I highly doubt it. Although they have nukes, they don't have ones big enough/enough in quantity to wipe out our whole country. If they were to attack us, we would have more than enough firepower/time to retaliate from surviving parts of the country and decimate them. Such a small country provoking a much larger one with more firepower is a suicide wish. Not saying it's impossible but it's highly unlikely. Don't forget that US has intelligence agents over there too.
If the US is going to be engaged in a nuclear war, it will most likely not be with North Korea. Iran and China are more likely candidates.