It comes after Estonia's neighbour Russia called up reservists last week to boost numbers fighting in Ukraine.
Estonia -- Russia's neighbour and former state of the Soviet Union -- is conducting a six-day snap military exercise for more than 2,800 reservists.
It's an apparent countermove to Moscow's call-up of reservists last week.
The purpose of the defence readiness exercise is to practice the functioning of the reserve army, Estonia's defence ministry said.
"There is no direct security threat to Estonia," the ministry said in a statement.
In a bid to keep Estonia's 30,000 military reservists ready for combat, the Baltic nation traditionally schedules random war games once a year.
"The Estonian reserve-based defence model requires for reservists to be ready to react and participate in exercises at all times," the defence ministry said.
The exercises end on Wednesday.