This depends on which Android image you are using for your BPi.|
The Android 4.2 images available for BPi are rooted, but proper root control requires a root access manager. Some of the images prepared by forum member mattrix have the 'SuperSU' app added for this purpose, but it needs to be configured to work properly and that may need to be redone after updates. And if you didn't use his images then you'll have to install 'SuperSU' or some other such program yourself.
All Android 4.4 images seen so far (as released on another site) are NOT rooted. Installing SuperSU on these images will not help, as it can't access the root areas. If you are using one of these images and need root access, I know of no other way than to start over with an Android 4.2 image.
Best regards: dlanor