No, you do not pay tax on a withdrawal which is considered a loan from your retirement plan at work that you are repaying through payroll deductions. However, if for some reason you stop paying the money back (such as when you may leave the company), then any remaining balance on the loan becomes a distribution to you and that amount would be included in your taxable income.
If you are not asking about a loan, but something else, please add more details in a follow-up post.