Carter met with U.S. troops manning a Patriot missile battery deployed at the Turkish border with Syria. His visit follows what the U.S. State Department said was a terrorist attack on the U.S. Embassy in Ankara last week.
"We stand with the people and the government of Turkey and missile defense is just one way we are doing that," Carter was quoted by the Pentagon as saying.
Germany, the Netherlands and the United States responded to a Turkish request to NATO in December for military support to help defend against the Syrian civil war. Conflict in the Syria has spilled over the Turkish border at times.
NATO leaders stressed the deployment of Patriot batteries along the Turkish border was for defensive purposes only.
Last week's attack in Ankara left embassy guard Mustafa Akarsu and the bomber dead.
Civil war in Syria has left at least 60,000 people dead since conflict begin nearly two years ago.