Secretary-General Anders Fogh Rasmussen urged European governments that have sharply cut defence spending as they have trimmed their budgets to maintain their military capabilities.
The NATO leader said the unrest may harm local economies, spurring illegal migration to Europe.
Events in the Middle East and North Africa "serve as a timely reminder that we cannot take security for granted, even in our immediate neighbourhood," he said, urging European nations to keep their level of defence spending up.
The military alliance has so far refrained from commenting directly on the turmoil engulfing those two countries and other Western allies in the Middle East.
NATO cooperates closely with a group of friendly nations in the region, in a process known as the Mediterranean Dialogue. Besides Egypt and Tunisia, the group includes Algeria, Israel, Jordan, Morocco and Mauritania. NATO also has a separate cooperation agreement with a number of Persian Gulf states.
"Therefore, it's quite natural that we follow the situation in Egypt and other countries with great interest," Fogh Rasmussen said.
"But I don't consider the situation as a direct threat to NATO allies," he said. The alliance has no intention of intervening in the crises, he said.
Fogh Rasmussen also warned that the instability could harm the Mideast peace process. He is scheduled to travel to Israel this week to address an annual conference on security and international issues.