I work as a teller for credit union and have been in the financial business for more then five years, and I can tell you that JP Morgan Chase Bank checks are the most common check I see tha people deposit and do not know what they are for. Sometimes it is a check asking you to cash it and return funds to them by wire or money order, but in your case it sounds like it is from that bank for a credit card. Also known as a credit card check, mostly below the five dollar range, the check when cashed enrolls you in a credit card to avoid paperwork... and to scam you into something you probably didnt want in the first place. On the back of the check where you endorse, read what it says right below the endorsement line. It would say something to the effect "by accepting this check, you are agreeing...". If this is the case do not deposit it, unless you are interested but find out what you are signing up for.
Another thing I suggest is calling JP Morgan.
DO NOT CALL THE PHONE NUMBER ON THE CHECK!!!!!!
If it is a scam, that phone number is a fake and can hurt you. Look up their phone number online at their website for customer service. Ask the representative what the check is for, they may ask for teh check number. I would not give them any sensitive information, like your social. If this ends up being a credit card/loan/product/ check, ask them to take you off their mailer list and give them your address. Otherwise you may get these again. They are sneaky because they make it look so official, and delivered Fed-Ex.