From the ntp doc:
8. Authentication
Four commands require authentication to the
server: config-from-file, config, ifstats, and
reslist. An authkey file must be in place and a
control key declared in ntp.conf for these
commands to work.
If you are running as root or otherwise have
read access to the authkey and ntp.conf file,
ntpq will mine the required credentials for
you. Otherwise, you will be prompted to
enter a key ID and password.
Credentials once entered, are retained and
used for the duration of your ntpq session.