He made these remarks after meeting with the newly appointed top U.S. and NATO commander Gen. David Petraeus and visiting troops in Afghanistan.
"We are, in fact, making slow but steady progress toward out goals," the top U.S. commander added.
"Counterinsurgency fights have ups and downs, setbacks and steps forward," he said, adding, "But I am, to be frank, more optimistic than I have been in the past."
On the same day when Mullen toured Afghanistan, Taliban militants attacked police checkpoints and overrun Barg-e-Matal district in the county's eastern Nuristan province; while two days earlier on Friday the militants claimed capturing two U.S. soldiers in Logar province 60 km south of Afghan capital Kabul.