If some of the tickets in your registration site do not require payment a "Free" ticket label will appear. However you have the option to hide this label.
Once you have opened your registration page editor through hub.eventmobi.com and navigated to the "Tickets" menu, select the "Ticket Settings" tab. From here you will see an option to "Show 'Free' Label for free tickets". If you unselect this option, the "Free" label will no longer appear.