Imphal has been ranked 32 among 150 places which are most likely to have a terrorist attack. The rank is 1st in India with Kashmir trailing way behind somewhere around 42 in the world rank and 2nd in India, so one needs to be cautious not to get oneself into trouble.
During most of the time Imphal and its surroundings are relatively peaceful, but one needs to be extremely cautious during August 15th and January 26th of every year, for this is the time when the section of society which are against the merger of Manipur to India gets into several violent activities which includes planting IEDs and what not.
With the recent Attack on Chandel district in which 18 personnel of Dogra Regt.were killed, the situation is not so calm in the region.
If you are visiting the hill areas it is advisable to take the help of local people.