Howdy!
The book requires no other previous knowledge other than Java, and no Java beyond what is in Head First Java, so yes -- you're good to go with the EJB book. That is, assuming you really do want to learn about EJB. Of course, we think that *everyone* should have this book, even if they don't

but that's just a starving writer talking
Actually, if you're interested in distributed programming, some of the early parts of the book do cover a lot of background that's helpful even if you don't ultimately go down the EJB road, but still, most of the book is very EJB-specific. If you're interested and new to EJB, then I'd recommend the book regardless of whether you plan to take the exam -- you can use the mock exam questions to simply guage how well you're really learning the material. But EJB is not a technology that everyone will need, so unless you think there is really *some* reason why you might *some* day move in that direction, then there are probably other Java technologies that might be more helpful, like
servlets. (Of course, Head First Servlets is coming too

but not until next year).
Thanks for asking!
cheers,
Kathy