Both Uses

mischievous
in
Wonder, by R.J. Palacio
(Edited)

When his mouth went straight, he was being mischievous.
p. 89.9

mischievous = playfully causing minor trouble
"Are you Via's boyfriend?" Auggie asked mischievously, and his sister pulled his cap down over his face.
p. 184.5 *

mischievously = in a manner that playfully causes minor trouble

Definitions:

(1) (mischievous)
playfully causing minor trouble; or describing the smile of someone doing so

Much less commonly, mischievous can reference real harm without any sense of fun. But in modern writing, that usage has largely shifted to other words like malicious, destructive, or damaging.
(2) (meaning too rare to warrant focus)
In law, mischievous references a property crime such as vandalism or graffiti. Very rarely, the word can reference someone or something causing serious damage.

In archaic literature mischievous often refers to bad behavior without any connotation of playfulness or of the harm being minor.