I am an international student. I filed my federal tax return. But I have not mail the files related to state tax. Can I mail it on monday? I cannot do it online

Yes, you can mail in your state tax return on Monday.

Here's a link to State Dept. of Revenue's if you want more info on your state regulations. 

Yes, the due date is Monday, April 15.  The return must be post marked on or before Monday.