This most often means that the detector is working appropriately. However, every detector manufacturer uses their own specifications for developing detectors and you would be wise to read the instructions that came with yours to determine if this is correct. Some models have additional information about what the light status means inside of the detector cover.
Usually a blinking green light on a detector means that it is operating properly. However, if you have two identical ones and one is blinking while the other is not, try replacing the batteries. If that does not work, check the owner's manual or call the manufacturer for more information.
For most smoke detectors a blinking green light means that everything is okay with the smoke detector. On other smoke detectors it means that it has detected smoke at some point but that smoke has gone away. Your best bet is to look at the manufactures guide to check what it means or look your model up on the internet.
Typically a blinking green light is an indication that your smoke detector is in working order. If it is accompanied by a soft 'chirping' that indicates that your battery is low and should be replaced. Another possibility; smoke was detected, dissipated (think kitchen) and needs to be reset. Instructions can often be found on the back of the detector.
Did you ever determine why one smoke detector has blinking green light and the other has a steady green light? We have the same situation which we think started after a power outage.