Yes a 401K is taxable unless it was a ROTH 401K Account. 401K contributions come out of your wages pretax and aren't taxed until you take it out.
If you take a Withdrawal it is taxable on your return and may push you into a higher tax bracket and more income can reduce or eliminate some credits you may qualify for and may make more of any Social Security or SSDI taxable. So be careful. Then there is a 10% Early Withdrawal Penalty if you are under 59 1/2 or under 55 if you left that job. You can lose like up to 50% of it for taxes and penalties for federal and state.
