Not for all states. But, out of the 7 northeastern states, you will need permit for 3 of these states: Arunachal Pradesh, Nagaland, and Mizoram. This permit is called as Inner Line Permit (ILP). A permit can be obtained at any Arunachal Bhawan, Nagaland Bhawan, or Mizoram Bhawan, located outside of northaest. Major airports in northaest, like Guwahati international airport, have the facility of providing permits. The government of Arunachal Pradesh has also provided the facility of online application of Inner Line Permits. For foreign nationals, you will require another type of permit called as Protected Area Permit (PAP).
We usually include the cost of application for ILPs in the total cost of our tour packages to keep the tour hassle free for you.