Under "Federal Review" tab, my "Final amount that's taxed" is 0 already, but under "tax" there is still some amount 600+ to due. I am in OPT period and my form is 1099-MISC. Does anyone know what this is all about?

Thanks!

No one answered?

The $600+ amount was probably the self-employment taxes, which is the self-employed's version of FICA (Social Security and Medicare) taxes.