It's fine, but you might want to look into using better shampoos and conditioners. I probably have curlier hair than yours and I don't deal with much of any frizz. This is because of the products I use. Try different shampoos, conditioners and leave-ins and see which ones leave you with the least frizz. Try sulfate free shampoos if you're not already using them. They are less drying on your hair than regular shampoos.
How is your hair as far as dryness? Is it too dry? If so, this could also be a reason for your frizz. Dryness creates a lot of frizz, so make sure you give your hair enough moisture so that it can keep frizz to a minimum. I have a dry hair type, so I don't even use regular conditioner any more. I deep condition about 1-2 times a week to keep my hair moisturized. I use a leave-in conditioner daily to help with moisture, too.
To answer your question, yes you can leave regular conditioner in your hair. Be wary of protein though. If your hair starts to become dryer, brittle, and possibly break that's a sign of too much protein, possibly from the conditioner. Try switching to a different conditioner, using a leave-in conditioner instead, or cutting down on how often you use regular conditioner as a leave-in.