Some of modern-day Iran was very much a part of the Central Asian sphere of influence, and there was significant communication along the Silk Road. They were certainly aware of the steppe peoples, long before said peoples left the steppes.

I'm not an expert on medieval Islam -- so experts, feel free to offer more detail! -- Muslims -- were also significantly involved with Central Asian trade. The Islamic world very much included Central Asia, and as such, people were aware of the barbarians at the borders -- as Romans, even in Rome itself, might have been aware of Gauls.

However, it may depend on your definition of "Arab" -- intercontinental communication was more prevalent in urbanized, trade-dependent communities, and Arabia itself remained mostly feudal.

Sources: Lost Enlightenment: Central Asia's Golden Age from the Arab Conquest to Tamerlane (S. Frederick Starr) & Destiny Disrupted (Tamim Ansary)