Magma is sloshing around under Yellowstone, but there is no evidence that activity is trending upwards. Most of these big calderas see regular injections of magma from depth, followed by gradual withdrawals.
There was some worry a few years ago about a bulge under Yellowstone Lake which some people thought was due to magma rising towards the surface. In fact it is probably caused by hot water and gas rising up beneath the lake. It's not growing and not associated with any seismic activity. The biggest current risk in Yellowstone is a recurrence of the massive hydrothermal eruptions which have occurred in the last few thousand years (IIRC the latest has been provisionally dated to 1300 or so).
And its impossible to say what scale the activity in Yellowstone would be on, again caldera eruptions can be catastrophic, or they can be small scale eruptions of magma. A good example is in California where the mind-buggeringly big Long Valley caldera created a series of catastrophic eruptions around 760,000 years ago; but since then activity has been in the form of a series of smaller volcanoes at Mammoth Mountain and the Mono and Inyo Craters which wouldn't really be a threat to anyone.
The three big Yellowstone eruptions were 2.1 million, 1.3 million, and 640,000 years ago, so not exactly clockwork and there is no geologist who would ever say when an eruption will occur - only that one will occur at some point in the future.
Besides, why worry about Yellowstone when the Campi Flegrei caldera is only a 3 hour plane flight away; much more active and where the food is better?
But if you do ever get a chance to visit Yellowstone, take it, it is one of the most extraordinary places on Earth.