Sending humans to Mars is an explicit goal of NASA's Mars exploration program, but it comes second to other goals like finding potential life and understanding the planet's geology. Some sources say that NASA aims to send humans to Mars by 2035, but as of February 2015 NASA's official Mars exploration website does not confirm this. It's likely that budgetary and management challenges have made it difficult for NASA to officially announce this timeline.
NASA representatives affirmed that they hope to send astronauts to Mars by 2035, according to a 2014 article from the Houston Chronicle. This article confirms that NASA scientists remain committed to the Mars exploration program. However, these scientists hinted that the United States would likely need international cooperation to achieve this goal. The first manned mission to Mars would take around 3 years, including travel to and from the planet.