Yes. Converting a sole proprietorship or a partnership to an LLC is an easy way for sole proprietors and partners to protect their personal assets without changing the way their business income is taxed.
Some states provide a simple form for converting a partnership to an LLC (often called a "certificate of conversion"). Sole proprietors and partners in states that don't provide a conversion form must file regular articles of organization to create an LLC.
In some states, before a partnership can officially convert to an LLC, it must publish a notice in a local newspaper that the partnership is being terminated. And in all states, you'll have to transfer all identification numbers, licenses, and permits to the name of your new LLC, including:
For general information on forming an LLC, read Nolo's article How to Form an LLC.