To control access to groups it is necessary to add another field to a group type. From the Organic Group configuration page, click on OG field settings.
This next page requires some careful study. If you have already added a field for Group roles and permissions this should be easier to understand. The goal is to add a field to the group type that will allow the control of access to a group. First, select the group type from the select list labelled Bundles. Next select the Group visibility option in the Fields list. Third, click the Add field button. Lastly, the new field will appear in the table of groups-related fields associated with the group type.
To confirm this field has been added, navigate to the Manage Fields tab on the content type (e.g. /admin/structure/types/manage/group/fields) There you will see the new field with the maching name of group_access.
Next, go to a group page and click on the Edit tab. You will see the new field in the edit group form. Select Private - accessible only to group members and save the group.
Notice the group page now indicates this new setting.
Now, if you view the Group page as an anonymous user (or a user who is not a member of the group or who does not have administrator permissions) you will get an Access Denied message.