I agree with Claire - I think in older texts it's a directly negative term, but you'll see it used affectionately in modern use (eg. little rascal / old rascal / saucy rascal). It's like saying that person's naughtiness is almost cute.

It can mean either. It all depends on the context, the tone it was used and how it is intended. For an example, a girl friend chiding her boy friend, "You are a rascal and a scalawag!" It can mean either way! So you need to find out the acutal reason why it was being said. Worse still, if it was said, "Sir, you are a rascal and a scalaway!", then you will have to study the body language as well!

It's as Regina says, but I'd say this use is old fashioned. Oxford has 'a mischievous or impudent child' as the first meaning with the Merriam-Webster meaning as the second one. I'd say that, when applied to a child, it's actually affectionate. Actually, when I was little, I had a teddy bear in a t-shirt that had 'I'm a little rascal' written on it. :)

Merriam-Webster gives this definition of rascal- a mean, unprincipled, or dishonest person or a mischievous person or animal. This basically gives you an idea whether it's negative or positive.:)