All income must be reported on your tax return regardless of how small the amount. If the 1099 was a 1099-MISC and it was your only income, you would have to file a tax return for it if the amount was over $400 in order to pay 15.3% self employment tax.
All of your income must be reported on the same tax return. If you already filed a tax return without the 1099 and it was accepted, you will have to amend your return to add the 1099.