Yes. You need to report all taxable income on your income tax return. This would include $400 of miscellaneous self-employment income even if you did not receive a 1099-MISC.
The $400 limit relates to your self-employment income being subject to self-employment taxes (not income taxes). According to the IRS, you usually must pay self-employment tax if you had net earnings from self-employment of $400 or more.
