If you reported self-employment income on your return, that income is subject to both income tax and self-employment tax. If your return is showing $0 taxable income, that means that you are not subject to any income tax.
Self-employment tax is separate and based only on your self-employment income. So, you can still owe self-employment tax even when your taxable income is $0.
Take a look at the following TurboTax information to learn more about self-employment tax:
What is the self-employment tax?