If you are using the HearLink PLUS Bluetooth transmitter to stream the television audio to your BeHear headset, the answer is yes.
A quick press on the middle button of the headset (left-hand side for NOW or ACCESS, right-hand side for PROXY) will mute the TV audio. Another quick press on the same button will unmute the sound. [Note that television audio is muted automatically if you receive a call to a smartphone that is paired to the headset (in parallel to the HearLink PLUS connection). Once you either reject or terminate the call the TV audio will resume automatically.]
If the television has built-in Bluetooth support, allowing you to connect your BeHear headset directly to it, you may also be able to mute and unmute the TV audio stream from the headset, as described in the previous paragraph. Consult the TV's technical documentation.