Maybe, but it could also be nothing. There may be something in your tax return for which the IRS needs additional documentation or they may have a different calculation. There may be a difference in the information you provided and the forms provided directly to their agency (such as your W2). Without knowing more about your tax return, it is hard to guess what the issue may be.
The IRS cannot change the amount of tax due or refund without providing notice of the specific portion of your tax return and why they disagree with your calculation.
In the next 30 days, you need to gather all your tax documents. If you have not printed a copy of all your forms, do so, including your tax return.
For more information, follow this link: Understanding Your IRS Notice