In general, if you have not begun business activities and have no expenses and no income, there is no requirement to file a tax return. However, as LLCs are controlled by state law, you may have some kind of filing or registration requirement in your state.
Also note that when you do begin business activities, your filing requirements will be very different depending on if this is a single member LLC, and LLC with your spouse (and in which state) or an LLC with other people. If you need more information, let us know.