I have 2y stable auto immune hepatitis ast and alt always <30, however in 2 months plats went down from 185 to 124 after mebendazole, should i worry?

Concern reasonable : Your platelet count should be followed to ensure returns back up to normal and not continue to drop. If ast and alt normal still unlikely due to your aih but could be related to Mebendazole or unrelated transient drop due to intercurrent illness such as a virus. You didn't say if you are on medication for aih and that would be important to know as these meds can drop platelet counts sometimes.