Well, you have them now courtesy of your soil supplier. What is "normal" depends on what the seller has. You can get all kinds of noxious weeds from soil vendors. Stinging nettles are particularly noxious, but some people actually cultivate them in their gardens for a "natural" approach.
Nettles are prolific growers and spring from underground rhizomes . These underground horizontal root stems can spread 5 feet (1.5 m.) or more in a season, continually re-growing from the rhizomes, even when broken apart. Tilling or cultivating may actually spread the rhizomes, increasing the infestation. Glyphospate works on them but repeated applications over time will be required.