What race were the Scythians?

The Scythians were believed to be of Iranian origin. They spoke a language of the Scythian branch of the Iranian languages. The group of Scythians that made its way to India were known as the Indo-Scythians or Shakas

For further reading check the following articles:

• Facts about Kushan Empire
• UPSC IAS Prelims Examination: Important Dynasties and kingdoms of Ancient India