Raw gyro values are quite high even when still

-5.92041 -0.39673 0.79346
-6.01196 -0.09155 0.76294
-5.95093 0.15259 0.82397
-6.13403 -0.09155 0.70190
.
.
.
..
-5.88989 -0.33569 0.79346
-6.10352 -0.24414 0.82397
-6.04248 -0.15259 0.79346
-6.04248 -0.27466 0.82397
-6.01196 -0.39673 0.85449
-6.01196 -0.33569 0.79346
-6.07300 -0.36621 0.73242
-6.04248 -0.33569 0.97656
-5.95093 -0.39673 0.85449

Above are the raw gyro values which I get from an Ardunio Duelinove connected to an MPU9150 breakout when the MPU is still. These values are straight from the sensor registers and converted to DPS on board, communicated serially to the PC and printed to a file.

I think the gyros are auto-calibrated by the board and I get a non zero offset when I query for it from the offset registers. Even then it is inaccurate. How can I make sure my gyro offsets are accurate enough to get zero values when it is still?