Question / Help Desktop audio going through mic

I downloaded OBS recently, and I've been following along tutorials on YouTube setting it up for recording only, no streaming. I have all my audio and my video coming in and it's nearly ready to start recording, however, when I did a test recording, any audio that would come in from my "Desktop" input would play through my mic, and in turn you can hear a faint echo in the recording. Can anyone help me fix this so that my desktop audio will not play through my mic? Please and thank you.
 
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