It depends on what you think is a bubble is.
If you think a bubble is something that reaches a high price and suddenly loses price for any reason, than yes, it is a bubble, and "popped" a lot of times. But always started to be inflated again and became bigger than is was before.
But if think a bubble is something that is priced higher than it should be, and it would make the bubble explode, no, it is not a bubble. I think Bitcoin can be priced a lot higher than is is right now, because just a very small fraction of world population knows about bitcoin.
Everyone knows what gold is. They know gold is a rare metal and a limited resource, but nobody knows when it will not be found anymore on gold mines, and that's what makes gold to be so valuable. But Bitcoins is more "predictable". We know that only 21 billion Bitcoins will be mined. Now, imagine what would be Bitcoin price if at least 10% of the world knew about it and wanted to have it?
Asking whether bitcoin is bubble is so nonsense as asking whether gold is a bubble, in my opinion. Bitcoin is the "new gold".