Generally, as a people, no, American Indians are not mean. However, just like some Irish people are mean or some German people are mean or some black people are mean, some Indian people are mean. Some people of every race are mean. American Indians, like all people, have unique personalities.
Native Americans are people first. Some Native Americans have been perceived as being mean, when they have drank too much. Every race has people that can be mean and are perceived as being a mean race.
I have met Native Americans and they were as nice, as any other person, from any other race that exists, on the planet Earth.