What are your standard deductions set to? That effects if you owe money or not. Also if you had unemployment income and taxes weren't deducted from that, that would effect if you are owed taxes or if you owe taxes.
There can be any number of reasons, but the most likely is that you claimed too many allowances on your Form W-4.
Claiming too many allowances results in too little withholding from your paycheck, and eventually owing money once you file your tax return.
Another possibility that's very common this year is if you received unemployment benefits, but had no taxes withheld from it.
We're unable to see your return in this forum, so we can only speculate.
Please see the resources below for more information.