You will need to notify the IRS. Unfortunately, there is nothing you can do to stop them.
When you file your own return, there will be a discrepancy, since someone claimed you and you also claimed yourself. The IRS will send letters and that person will have to justify claimining you. If you choose not to wait for this long process, you can try to contact the IRS.
If they file first and get Accepted your return will reject. If yours rejects you will have to print and mail to claim yourself.
Who is claiming you? If it's your parents they might qualify to claim you if you are under 24 and a full time student.