I recently withdrew my 401K through John Hancock Investments. At the point of withdraw, I was taxed federal. Is it possible to owe more than what 1099-R form says?

Yes.

You didn't pay the tax, you had tax withheld, just like W-2 withholding that will be applied now to pay the tax.

The actual tax depends on your other income and margional tax bracket. If not enough tax was withheld, you will owe more.

The box 4 (or box 12 state) withholding will be added to all other withholding, such as W-2 withholding, and be shown on line 64 on the 1040 form to offset your overall tax liability. If you are not 59 1/2 or older the there will be an additional 10% early withdrawal penalty.