inaccuracy of mlx90614 temperature sensor

Since the MLX90614 is factory calibrated you should not face this problem. Try using a different sensor. How much variation are you getting it is less than 0.5*C then there is nothing much we can do to correct it. 

Using Melexis IR temperature sensors with arduino, especially with arduino UNO and arduino nano, there are some limitations and as well as it takes time to calibrate the sensor with our main controller. Once the calibration done, you can check the object's temperature. I've similar issue in my hobby project, for that I contacted with SSLA technical support team and got my issue resolved.

I am also facing this issue in my project. The object temperature varying with change in ambient temperature. Kindly help me out

How you wired the sensor? What is the placement? How far is the object you are emasuring?

In the range of 0-120ć, MLX90614 measurement accuracy can reach 0.5ć, for the body temperature measurement of about 37ć, the measurement accuracy can be up to about 0.1ć. The laser distance measuring module consists of VL53L0X laser temperature sensor.