the same is for pos then you need your cpu usage for running a pos coin, yeah is very little compared to regular mining, but it is always mining, just energy efficient....
As PoW coin energy requirements go up exponentially, energy requirements of public PoS nodes stay about the same, and are going from 1% of a PoW coin network's requirements to 0.1%, then to 0.01%, etc.
For non-public nodes, you use your computer anyway, running a browser to forge doesn't take any additional energy.