Several flight crews operated a Q400 from which Maintenance had removed the required EFBs but had failed to log their removal in the logbook. The flight crews assumed the mounts had been installed in preparation for installing the EFBs and because there was no log item; operated the airplane without questioning their absence.

Narrative

I was called at home by the Captain who had taken over our airplane after we left it. Earlier; when we departed on our trip; we did not have any open write-ups in the maintenance log nor any MEL about the Electronic Flight Bags (EFBs) not being installed. Paperwork was all in order. I did notice that there were EFB mounts installed on the aircraft; however; there were no EFBs on the mounts. Apparently; as I found out after-the-fact; Maintenance had removed the EFBs and failed to enter anything into the maintenance logbook. The new Captain had decided to call Maintenance Control to inquire about the missing EFBs and learned the aircraft was actually not airworthy due to the removed EFBs.I obviously had seen the EFB mount without the EFB; but didn't think twice about it because I figured that Maintenance had simply installed the mount to be ready for installing the EFB at a later date; and; with nothing written in the logbook; I figured there was no problem. I'm filing this report about the event for myself; however; I know that we had taken the airplane from yet another crew who had flown the airplane and; before that; who knows how many people had flown this airplane.