Most likely it is ... but you can call the number on the notice if you wish ... or call the IRS here ( be prepared to be on hold for a long long time ) ...
Call the IRS: 1-800-829-1040 hours 7 AM - 7 PM local time Monday-Friday
When calling the IRS do NOT choose the first option re: "Refund", or it will send you to an automated phone line.
