If you would prefer to not hear the microphone input, you can set the Microphone Monitor Mode option to Direct monitor (recording and broadcasting only). This will still mix the microphone input with your recorded and broadcasted mixes, but it will not mix the microphone with the Master output. Don’t forget to press the Talk button when using the microphone if you use this option.
Open - Preferences - Sound Hardware - Microphone Monitor Mode - Change to Direct monitor (recording and broadcasting only)