Depends on where you live in the US or Canada.
I always assumed that it was flat out illegal. Turns out that there are some US States that do not have a prohibition against it. As I write this with music playing on my headphones, they’re at a volume that you could carry on a complex conversation with me, but I don’t think I’d want to try that while driving.
On the other hand, I drive a Jeep Wrangler. Wonderful car but once you get above 55 MPH with the roof off, and I do that every chance I can, hearing the radio or the person in the next seat is a chance thing. These cars can be noisy, as in teeth rattlingly loud.
There are many people who wear hearing aids, maybe because they drove a car with their radio habitually too loud. Boom Cars come to mind. You know the sort, some clown that removed the back seat of the car just to place Kicker Boxes with giant speakers in them larger than anyone would need in their home. They crank the music up so loud that they vibrate the license plate on your car next to them at a stop light. Too bad it won’t stop them from having children.
I could legally buy a pair of seats that have speakers in the head rests. In fact, if I had a spare $250 it would be worth it because it sometimes is necessary to drive the speed limit on the highway here in Florida, and the Turnpike is 70MPH all the way through the South Florida Sprawl. Those little speakers next to your ears would be as dangerous as a pair of non sealed headsets or ear buds.
When I rode my motorcycle, as a rule, I had earplugs in my ear. Talk about loud! I guess it’s just lucky I never got caught.
At any rate, turn down the radio, leave the headphones to the passenger since it may shut them up so you can concentrate on your OWN driving, and turn off the cell phone. It’s not an office, it’s not a beauty parlor, and it’s not a restaurant. It is a vehicle. Be safe out there, the life you save may be mine.
In the meantime I think I’ll turn down the music in here. I can’t hear the birds singing outside.