To some level, yes. I think that cryptocurrencies are a threat to government control over the economy. Let's look at what cryptocurrencies are: they're digital representations of value (like money), only they're not controlled or regulated by any state entity. So if you have bitcoins, for example, you own them—but nobody else does. You can't turn them into cash or use them as collateral for loans.
This means that governments don't have any control over how much money is in circulation, or who has access to it. And that means that governments can't use monetary policy to affect the economy. For one thing, governments can't print more money when there's inflation because they don't have access to bitcoin! If there were an influx of bitcoins on the market and lots of people were buying them up, then the price would go up—but the government wouldn't be able to print more bitcoins to make up for it.
So instead they'd have to raise taxes or cut spending instead—which would probably hurt their economy even more than inflation would have been hurting it otherwise! This happened with Zimbabwe's dollar when it collapsed in 2008.