Mandalas originated in India, but were mainly used in Tibetian Buddhism. Below are some quotes from various web sites (featured at the bottom of the page) regarding the origins of mandalas:
-Tibetans became familiar with the mandala early in their introduction to Buddhist art and culture, a process begun with the first ruler of the historical period, Songtsen Gampo (srong-btsan sgam-po, d. 649).
-Mandalas existed at early Buddhist centers in central Asia, e.g. Dunhuang and Khotan, both frequented by Tibetans during the eighth and ninth centuries.
-Samye (bsam-yas), Tibet's first monastery founded ca. 779, was based on the architectural principles of a three-dimensional mandala, reportedly following the plan of Uddandapura monastery in eastern India.
-Many such texts, crucial to the identification and interpretation of the mandala, were translated into Tibetan from Sanskrit and can be found in a portion of the Tibetan Buddhist canon known as the Tanjur (bstan-'gyur).
-According to Buddhist history, the purpose, meanings, and techniques involved in the spiritual art of sand mandala painting were taught by Shakyamuni, the historical Buddha in the sixth century B.C. in India