It depends.

I will assume that you are still employed at the company where your 401(k) is. If that is true, there may be a few ways to take a withdrawal from your 401(k).

The first is a loan. You didn't state whether or not you would consider this but, if your plan allows loans, you could take a loan and pay off your mortgage with it. The problem is you would have to pay this back to yourself, plus interest, over a 5 year term. Your plan might allow a longer term up to 30 years for purchase of a home, but not payoff of a mortgage. If you have a large balance these loan payments back to yourself would be huge.

The second is a hardship distribution. If you qualify (which is up to your employer or plan sponsor who are usually one in the same) you could take a distribution from your plan as a hardship distribution to pay your mortgage. Your plan would have to allow this distribution type and you would have to apply, but the prevention of eviction from a home is one of the valid reason to qualify for it.

The third is it you can simply take a distribution for any purpose. This might be the case if you are over 59.5 years old or if you are no longer employed by the company. In that case, you could simple take a distribution and payoff your mortgage.

The best idea is leaving your 401(k) for retirement, but if you must, these are the options that might be available to you. To determine exactly whether your plan allows loans or hardships, check the summary plan description, which you should have been given as a participant. If not, you are entitled to a copy. You can also ask your employer or plan sponsor which of these are options for you and what the process is to apply for the distributions.

Using a 401(k) is a very expensive way to pay off a mortgage. The distribution (if you can get one, it depends on your company's plan) would be subject to your regular income tax, and a 10% penalty if you are under 59 1/2.

It might be cheaper to reduce the amount you contribute to the 401(k), and use the extra in your paycheck to make principal payments against your loan. This requires a lot more discipline but can knock months or years off your mortgage payments.