Possibly. Let's say your reaction is

$$\ce{D -> E}$$

You inhibitor could catalyse an additional reaction

$$\ce{C <<=> D}$$ 

If the equillibrium of that reaction was well on the left side, that would slow down the original reaction quite a bit.

Alternatively, it could catalyse a reaction $\ce{D->B}$, where B had an additional pathway

$$\ce{E <- B <- D -> E}$$

, which might be slow. 

This is all however very hypothetical. I cannot name an example for either.

Generally, if you find that something acts as an inhibitor, that means the reactions was already catalysed, and your inhibitor either permanently poisons the catalyst, or reversibly converts it into an inactive form.