If there were relatively few impressions , lets say between 15 - 30 , and you get two clicks, would you assume someone is working on click bombing you or some family member or friend trying to help you out? Have invalid clicks ever been an issue with you? One day, someone click 9 of my adsense ads and none of them were valid. Someone must not like me.
Ofcourse it is , but i am afraid if they want to play with your adsense account and click more than say 100 clicks on adsense , i think it will create your problem but 2 clicks is not an issue
If you get a lot of clicks from the same ISP Google will tend to make all or at least some of them invalid.
We can't say right a way it is normal or abnormal...it is depends on your daily clicks volume..if suddenly clicks volume increased then some one intenstionally doing click bombing..That is you have judge your self by taking your site analytics..