Not really. You can however work around it by using a reverse proxy,
and HTTP authentication in the reverse proxy.
Use auth.type = HTTP in gerrit.config, and have your reverse proxy web
server authenticate the users through a password file. Only users in
the file can register an account.
See [1] and [2] for more details.
[1] http://gerrit.googlecode.com/svn/documentation/2.1.2/config-sso.html#toc2
[2] http://gerrit.googlecode.com/svn/documentation/2.1.2/config-apache2.html
Another option is to just allow any user to register an account, but
use project level access controls to only permit users of some group
to read the projects. Even if a user registers, they can't see
anything without having an administrator add them to the group.