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.