A PC headset is designed to connect into a PC and often will not function correctly if connected to another device (like a mixing board). The difference between the mic input on a computer and a mic input on a mixing board is the power that is present.
A computer outputs about 5 vDC out of the microphone input which is the small amount of power that the microphone designed for a computer will need to work. In comparison a mixing board will typically output 48v Phantom Power which is too much for the microphone found on PC models to use.
Theoretically speaking you could use an adapter (like the MZA 900 P) to convert the mixer's 48v Phantom Power down to a much lower level power and potentially connect a microphone. This is the type of adapter you would use if you were trying to hardwire a lavalier microphone. The drawback to this solution is that the MZA 900 P is expensive (about $160) and while it will work well for a lavalier microphone which is designed for this purpose the microphone quality of a product like a PC headset will not be particularly great because it is designed to connect directly into a computer that has the correct power not run through an adapter that is converting power.
If you need a headset to connect directly into a mixing board it would be recommended that you consider a model that is specifically designed for this purpose like the HMD 26-600-XQ or the HMD 280-XQ.