If you have a single member LLC you are a disregarded entity for tax purposes and report you self-employment income and expenses on Schedule C.  If your single-member LLC did not have any business activity and does not have any expenses to deduct, you do not have to file Schedule C to report you LLC’s income.

If the LLC has more than one member, it is taxed as a Partnership. An LLC with no business activity that is taxed as a partnership is not required to file a partnership tax return unless there are expenses or credits that the LLC wants to claim.

Finally, if you have an LLC that has elected to be treated as an S-Corp for tax purposes it has the same filing requirements as a Corporation.  Therefore it must file a federal income tax return even if the LLC did not engage in any business during the year.