There are a number of reasons why the payoff balance may be higher than the amount shown on your monthly statement.
The most-common reason is that your monthly statement does not show the amount of daily interest accruing on your mortgage. Many times, this additional interest accounts for the difference between the final payoff and the statement balance. There are, however, other factors that can affect your payoff: there may be a shortage in an escrow account, there may be owed late fees or other lender charges, or there may be a prepayment penalty associated with your mortgage.
We always obtain a written payoff statement from your mortgage company, and will happily give you a copy if you want one.