Yes, there is an app for exactly that and much more called 'GravityBox' (it is an Xposed module). 

For information on how to install it, view a similar post [here](http://android.stackexchange.com/a/62206/52084)

**Alternatively**

If you are lucky your Phone app should have a "Blacklist" to which you can add numbers and prevent calls and/or messages (notifications) from them.