Yes, unless you take one of two feats. The other answers explain this more completely, but for completeness sake, I will reiterate:
- Under normal circumstances, due to the fact that the Net is a ranged weapon with a range of 5', you will be at disadvantage attacking with it. There are many ways to negate disadvantage by either doubling down while disadvantaged as Doug mentioned, or by using then net while you possess advantage.
However, there are two feats that you can take to make nets useful and to not have to deal with disadvantage while using them.
The first is Crossbow Expert, yeah that seems a bit weird, doesn't it? But in reality, this feat is perfect for the net wielder, as it negates the disadvantage from close range, and it lets you score an additional attack on someone when you attack, which you miss out on with your net attack as you can't use extra attacks after attacking with it.
The second is Sharpshooter. This is the favorite of the ranged net caster. It allows you to attack from long range without being at disadvantage. It also ignores cover. The damage feature of the feat is lost on the net user, but it does negate the disadvantage inherent in using a net.
So while under normal circumstances attacks with the net are always at disadvantage, it is something that you can get out of, you just have to spend resources on it. Whether that is worth it is quite debatable as the net is still quite weak.