what does it mean? --485 background check

Called USCIS and received the following message for my I-485:

"The processing of your case has been delayed. A check of our records establishes that your case is not yet ready for decision, as the required investigation into your background remains open. Until the background investigation is completed, we cannot move forward on your case. These background checks are required to be completed on all applicants who apply for the immigration benefit you are seeking. We will make every effort to make a decision on this case as soon as the background checks are complete. If you do not receive a decision or other notice of action from us within 6 months...."

Does it mean that the FBI fingerprint is still not done? How long do I have to wait? Does anybody have or hear about this situation? Please help me.