It depends on your computer. It should be safe, but some of those ports (depending on the manufacturer) don't put out a lot of power/current. They're pretty much guaranteed to be 5V, but they could be maybe 1A (5W) max output. The older USB-A standard was 5V/0.5A (2.5W) but that's not terribly common any more. A newer one should be able to output at least 0.9A (4.5W) although you'd need to find out if it could output more than that, where some do. Apple can put out quite a bit more than that when connected to an iPad. Mine says that it has 2.1A (10.5W) available for an iPad when I check in System Report. But it goes down if I have something else connected at the same time, like an iPhone or another iPad.
A newer iPad will come with a USB-C power adapter that's 5V/3A (15W) or 9V/2.22A (20W). Your computer won't have that amount of power available via USB-A, but it's hard to know how much without an inline USB meter.