According to http://en.wikipedia.org/wiki/Central_Asia:
The UNESCO general history of Central Asia, written just before the collapse of the USSR, defines the region based on climate and uses far larger borders. According to it, Central Asia includes Mongolia, Tibet, northeast Iran (Golestan, North Khorasan and Razavi provinces), Afghanistan, Northern Areas, N.W.F.P., Azad Kashmir and Punjab provinces of Pakistan, Punjab, Kashmir and Ladakh of India, central-east Russia south of the Taiga, and the former Central Asian Soviet republics (the five “Stans” of the former Soviet Union i.e. Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Uzbekistan).
Interesting reading material: http://enews.fergananews.com/article.php?id=2520
Iranian academician Mehdi Sanai wrote in his book “Relations between Iran and Central Asian countries” that first contacts between the two regions “predate Islam and even Christianity”. They originated in the period when “… a larger part of what is Central Asia nowadays was part of the Persian civilization. Embracing the ancient Iranian system of education, Central Asian schools nurtured great scientists. Islamic culture, science, machinery, education, philosophy, art, and literature owe their successful development in the region to this system. Even when governed by the Turk rulers who never stood for proliferation of Shi’ah Islam, the Iranians wielded considerable clout with the political and cultural life of the region.” Once Islam made its way into Central Asia, the regional culture and civilization became associated with Iran. Languages of Central Asian peoples include lots of Persian words. The locals make use of a great deal of Persian proverbs and verses.
Personally, I don’t have any idea. Somehow I feel that Iranians are Asians like the rest of us in the continent, but sometimes I think Iranians look like Middle Eastern (or even European), physically speaking.