If I am 70 1/2 and still working and participating in a 401k program, am I required to take a RMD from that account?

If you are still employed you are exempt from required withdrawals from that employer's 401K and you can still contribute to it if you wish. 

Note that if you are a more than 5% owner of the company, you are required by statute to take distributions from the 401(k) even though you are still working for the company providing the plan.

Some plans require all employees to begin receiving RMDs with the year in which the employee reaches age 70½, but if these distributions are not otherwise required by statute, these plan-required distributions would be eligible for rollover.