Yes, there is a provision of negative marking in the UPSC IAS exam and the marking scheme is as follows:
For Prelims : Every wrong answer will cost you 1/3rd of the marks for that answer, i.e., 0.66 marks for Paper 1 (GS) and 0.83 marks for Paper 2 (CSAT).
For Mains and Interview: There is no negative marking in these two stages.