Yes — that is normal for a reversed lens. When mounted backwards, the camera no longer has electronic control of the lens, so it reports no aperture information (often shown as F00).

Focusing also changes completely: a reversed lens only focuses at a very short distance, so you must move the whole camera/lens very close to the subject and fine-tune focus by moving back and forth. The focus ring may have little or no useful effect in this setup.

Depth of field in reverse macro is extremely shallow, so using a smaller aperture helps, but with Canon EF-style lenses there is no manual aperture ring. A common workaround is to set the aperture on the camera, press and hold the depth-of-field preview button, and remove the lens while the aperture is stopped down so it stays there. Some people also physically hold the aperture lever in position.

You’ll need plenty of light or longer exposures. Also, shorter focal lengths focus even closer when reversed, and adding extension tubes increases magnification further.