To create a new group in *nix machines, you can use
/usr/sbin/groupadd
You need to be root to use this.

However, in FreeBSD, this option doesnt exist.
In a FreeBSD machine, you need to edit /etc/group file to add a new group.
or you can use pw command to the same effect.

http://www.freebsd.org/doc/handbook/users-groups.html