There will be NBA games just like there are on all major supports, because there's a market for it.
Especially on a new platform like the 3DS.
Anyhow if you wanna find out, just head over to GameFAQs in the 3DS Sports game section and see if there's anything NBA.
As of today (Nov 10th, 2010) I don't see any NBA games in the list but it will probably change soon so just click the link below...
http://www.gamefaqs.com/3ds/list-43