A school bus? NO! NRS 202.265
A RTC bus? Local CAT busses are part of the RTC system. According to their own web site, they are a government agency, which makes them subject to preemption under NRS 244.364, NRS 268.418, and NRS 269.222.
RTC might have you think guns are prohibited the way they phrase rules on their website - http://www.rtcsnv.com/transit/rules.cfm:
NEVADA STATE LAWS ON BUS CONDUCT:Reading NRS 200.471, it's clear that the "present ability to use a deadly weapon" is requisite of an assault occurring. The way RTC phrases it, it implies that merely having the ability to use a deadly weapon is criminal.
Under Nevada Revised Statute 200.471, a person who commits an assault upon a transit operator with a deadly weapon or presents the ability to use a deadly weapon is subject to imprisonment in the state prison for a minimum term of not less than one (1) year and a maximum term of not more than six (6) years, or a fine of not more than $5,000, or both fine and imprisonment.
I have heard of no cases in Nevada in which this issue was tested. I know of a case in Virginia in which OCDO member danbus was ejected from a bus in Hampton, VA and the police called for his OC. He won and was able to ride the bus OC.
Anyway, bus drivers are likely to know less about the law than law enforcement, and we know the cops can't get it right, so don't expect every bus driver to be welcoming of guns on their bus. If they try to kick you off, be polite but refuse, and insist they call the police if they feel you are breaking the law. If the police ask you to get off the bus, comply, and let the bus drive away, just get on the next one. Probably not the best course of action if you're in a hurry, but change is slow.