How common were bear attacks on Native Americans in North America during Pre-Columbian times? Without firearms were arrows and knives sufficient defense against the larger bears, like brown bears?

You may want to reconsider resubmitting this question with a more specific place and time. The pre-Columbian period spans at least 20,000 years with changes in the kinds of animals and their distribution over time. Not to mention that North America is vast, it stretches from the Arctic in the north to present day Panama in the south. If we left the broad parameters as it is, an acceptable answer would be that there were virtually no bear attacks in the 15th century from Central Mexico on south to Panama because there are no bears in those areas at that time. But my guess is that is not the answer you are looking for.