The fact that it was not intentional may be considered attenuating circumstance in some cases but it will not save you of paying some fines
In order for them to initiate a audit they must have some evidence that fraud occurred.
The "evidence" can come from MANY sources, but there must be a discrepancy in your taxes.
They will not simply audit random people who may or may not have bought/sold bitcoins. If you were intelligent enough to trade your bitcoins in a pseudo-anonymous format, they will never know.
That all said, if they have some evidence you have been dealing in bitcoins that you never reported, you will likely be audited, and you will have to prove that you have never traded bitcoins.