If he calls you on your work phone, then yes, it is a unprofessional, except if he has no other infos to reach you (mail, personal phone, etc...).
I would not raise the red flag for that, but the recruiter seems really hungry. Double check any opportunity he might propose you, he may be just a bit inexperienced, or just really interested in your profile.
As keshlam said, the problem might that may only be "cold calls" just trying to get you signed up rather than actually having a position that they are recruiting for.
If you are interested, tell them to call you back on your personal line and on your own time; if you aren't, tell them to go away.
On the contrary, and to be a bit more generalist, if it is your personal phone, people just expect you not to answer the call (and call back later), or give a short response like "I am currently at work, please call me back later".
In that way, I don't think it's unprofessional, especially if it was the initial call.
Sometimes, the recruiter will leave you a message on your phone, that did happen to me several times.