If a female cat is pregnant will she still mate with a male cat?

No. A female cat will only mate while she is in season. Once a mating is successful and kittens conceived, the female will no longer be in season and will not do so again until the kittens are born and weaned off onto solid foods.

This is untrue, a female cat can mate and become pregnant as soon as a week after giving birth to a litter - she will also mate well into her pregnancy