Hi Nalaka,
Sadly there is no setting that can "Lock" the Headset button On. I am guessing that you must have a user who never turns the Headset button Off and only uses the "New Call or End Call Softkeys to control the phone. You will see that once the Headset button has been pressed it will stay on forever unless cancelled, even through a hard reset of the IP Phone.
The only configurable setting via CCM is;
"Enable Auto Answer on Headset" from the Directory Number Configuration for the specified device.
Hope this helps!
Rob