It depends on the privacy settings of the event.
From the Facebook help center
Events have several different privacy settings available to the host:
Public: Anyone can join and be added to the event guest list without receiving an invitation or being approved by a host. Anyone can see the event description, photos, Wall posts and videos.
Friends of Guests: Friends of a host and guests can join and be added to the event guest list without receiving an invitation or being approved by a host. They can also see the event description, photos, Wall posts and videos. Once a friend of the host has joined, their friends will also be able to join the event. Stories about the event will appear in friends' News Feeds.
Invite Only: These events can only be seen by people who have received invitations and can't be found in public search results. People who haven't been invited can't view the event description, Wall or photos.
By clicking More Options in the event creation window, the host of an invite only event can choose whether or not to allow guests to:
- Invite additional friends to the event
- Tag the event as their location
- See the guest list
Group Only: Group events are created within a group by a member or admin. The visibility of the event depends on the privacy setting of the group. Events created within open groups are visible to everyone and will appear in search results, but only group members can RSVP to these events. Events created within closed or secret groups are not visible or accessible to people outside of the group.