This article will show you how to mute your headset from the agent page. This is different from clicking Hold in that the lead will still be on the line and you will still be able to hear them.
On the Agent page look for the Green Telephone Icon Located on Upper left side of the page.
Click the Mute Button to switch off the mic.
To switch the Mic back on, Click again the Green Telephone Icon, and click on Unmute Button.