Post a photo. Get a 10x magnifying glass. Most likely you have spider mites; but you need a glass to see them. If you do a search here for spider mites, you will get lots of answers on how to treat them. Maybe most important is to put the tree in the shower about once a week to give it a good wash. Mites like dry and dirty (dusty) environments.

Undoubtably spider mites. As John has mentioned, hose it off well, either outside if temps are warm enough (not sure where you are, it's not in your "Zone" field), and then treat with an insecticidal soap spray which can be found at any big box store (Home Depot, Lowes), or on amazon.com. I think Safer is one of the better known brands. Continue hosing off several times a week about 6 or 7 times, followed by a spraying of the insecticidal soap spray, and you'll get rid of them. Check your other inside plants for a possible cross-infection, and treat the same.

Patty S.