Samsung Galaxy S3 camera light keeps flashing
S3 users have reported similar issue while receiving calls and alarm going off at AndroidCentral forums here. 

The solution posted there is to go to Settings &gt; My Device &gt; Accessibility &gt; Hearing &gt; Flash Notification

Un-check Flash Notification.

Even if the flash notification box is not checked, check it once and un-check it again. It should solve your problem.