Is ion activity in a salt solution pH-dependent?
Considering the effect of $\text{pH}$ on ion activity, one should take into account that $\ce{K+}$ and $\ce{Cl-}$ are respectively conjugated acid of a strong base and conjugated base of a strong acid. They are therefore both weak, with no influence on the $\text{pH}$. 

As a consequence, I would basically assume that also the other way round is true and that $\text{pH}$ has no effect on their activity.