The Oxford English Dictionary says the reflexive verb "behave oneself" is akin to what it calls the "modern" German verb "sich behaben". As far as I can tell, "sich benehmen" is a current locution and "sich behaben" is not. Is this a case of lexicographers considering something "modern" because it was used only five centuries ago? Or might it be more recent, e.g. two centuries?
dwds.de knows the verb behaben and defines it as follows:
To act or behave in a certain way
The part "Etymologie" on that page may be interesting for you as well. Deduced from that is the adjective behäbig, which translates to:
ponderous, sedate, stolid
Personally I've never heard behaben and even the Verb gehaben is rarely used today. The most common way it is used (even though crippled) is:
Hab dich nicht so!
Don't make such a fuss!
The only verb coming near to behaben is gehaben and the meaning would also match. Perhaps a typo?
In any case it would consider it dated in any meaning, not just in the behave counterpiece.