Is nonprofit required to allow public to sit in on Board Meeting?

I am not aware of any general rule that provides that a nonprofit corporation must open any portion of its Board meetings to the public. Some states have open meeting requirements for nonprofits receiving government funding or serving governmental purposes, but the situations are limited and not generally applicable to nonprofits as a whole. The ordinary nonprofit is a private entity and it is considered generous (if not foolish) to allow the public to attend or make comments at any time.