Facebook by default allows everyone to see friend list of any Facebook user. But if you do not want to share your friends list to anyone then you can hide it using the Facebook Privacy Settings.
Login to your Facebook account and click the drop down arrow below Account menu option.
From the drop down menus, select Privacy Settings.
In Choose Your Privacy Settings, click View Settings link.
In Connecting on Facebook screen, navigate to see your friend list. Click the drop down with text as Everyone and select Customize from the drop down list.
In the Custom Privacy Screen under Make this Visible to section, select Only Me option for These People drop down list.
By this way one can hide the friend list from any one in Facebook.