It's possible that you have missed entering some withholdings, or qualified for a deductions and not "claimed" it. I recommend caling the state tax authority and inquire about the details to make sure they are not in error. Otherwise, you will have to pay it back if/when they realize that it is.
https://ttlc.intuit.com/questions/1901670-how-do-i-contact-my-state-department-of-revenue
