Some civics have the security feature built in to the stock radio, so if you take it out, you lose your dome light and keyless entry (if you had that before). There are plugs/harness that will allow you to have both your aftermarket and stock radio plugged in at the same time. If you're handy, I belive you can wire it yourself.

I forget the brand of the harness that you can use, but it should be floating around here somewhere on the forum. That's how I found out about it for me.