What might be the problem when you are noticing bubbles coming out of your toilet when you take a shower? You might not think much about it, but this could actually be a sign of a serious problem with your plumbing system. What happens is called venting, and it is from air trying to find a way out of the system, and the normal vent being blocked for one reason or another.
There is a venting pipe that will let this air out, but it is quite possible that is has gotten blocked by debris getting in the pipe, or even a nest of a bird or rodent in there. You will need to have this blockage removed for your plumbing to work properly again. Sometimes this might require you to contact a plumber, but it is also possible to take care of it yourself if you have a snake or something similar that will reach the clog.