org-agenda-skip-archived-trees

org-agenda-skip-archived-trees is a variable defined in `org.el'.
Its value is

t

Documentation:
Non-nil means the agenda will skip any items located in archived trees.
An archived tree is a tree marked with the tag ARCHIVE. The use of this
variable is no longer recommended, you should leave it at the value t.
Instead, use the key `v' to cycle the archives-mode in the agenda.

You can customize this variable.