There are two ways to export Application Package in Eclipse using Android Tools -
Export Unsigned Application Package
Export Signed Application Package
Solution
Steps of generating an APK file using Eclipse -
Go to File > Export
From the Export window, go to Android > Export Android Application.
Click Browse... and select the Android Application project to Export.
Click Browse and select the debug.keystore. The default location for debug.key store on OSX is "/Users//.android/debug.keystore" and the password is "android". When you're ready to release your app to an application marketplace, you should use an existing keystore or create a new keystore.
Select the "androiddebugkey" alias and use "android" as the password.
Select a destination for the APK file and click Finish.
Now you are ready to upload and distribute the APK.