If you have an IRS tax lien against you, it's highly likely it is also placed against your home or a property that you own. The IRS files liens against people and businesses who owe taxes to protect their interest in case a property sells. Very often the sale of a home can full pay the IRS lien off. Other times only partially and in some "under-water" instances, won't be able to pay the IRS at all. As the buyer of your home will want to get the home "lien-free," you will need to get a "lien discharge" when selling your home.
Initiating a lien discharge with the IRS should get started when you have identified a buyer. Don't move forward until the buyer has been identified. It will take the IRS some 30-60 days to get the lien discharge to you upon submission, but this can vary depending on staffing and back-ups. You will need to initiate the lien discharge in the closest IRS office to you.