Can anyone shed some light in regard to the following situation:

I have a light outside controlled by one individual light switch. I
also have a light in our dining room that is controlled by a separate
individual light switch. When I turn on the switch for the light
outside, that light is extremely dim. What is interesting is that our
dining room light also turns on at the same time, although, it is also
dim. This light switch should not be turning on our dining room light.
Is the most likely scenario that something has been miswired? Just to
clarify, when I turn on the dining room light switch, it only turns on
the dining room light, so that works properly. Thanks in advance for
any suggestions.