Advanced Encryption Standard
what is the order of the matrix after mixed column step in 192 bit AES?


The only differences between AES-128 and AES-192 are


the key scheduling is different
AES-192 has two more rounds. 


There is no difference in any of the steps.

What you might be trying to look at is Rijndael with a 192 bit block size; there are differences in the shift row steps, which might be what you are looking at.  However, that has little to do with AES, which always has a 128 bit block size.