Yes

Hello,
Yes, you can use the NC (ant-noise) function alone and enjoy a moment of absolute silence.
Sony Support EN

Hi matiko,

Yes, you can use the noise cancellation even if you are not playing music. Auto Power Mode] is activated if no music is played after five minutes. Connect the headset to a playback device such as a mobile phone or MP3 player without playing music.
This prevents the headphones from entering [Auto Power Mode].

Sony Support EN