Depends on what type of EJB and what version of EJBs and if you use XDoclet to generate some of them for you.
EJB 2.x
Session beans need a Bean, Home and interface, but depending on how you wnat it to be accesses, the interface could be a remote or local or both, so the number changes.
Same really with Entity beans in general
EJB 3.x
One interface that you can mark as either remote, local, or both, or you can seperate and make one plain interface of neither type, then two other interfaces that extend the first and each one get their own @Remote or @Local.
Mark