Definition
To behave in a dishonest or mischievous way; to be engaged in activities that are not good or are likely to cause trouble.
行为不端；做不正当或不诚实的事
The group of teenagers was loitering suspiciously on the street corner, looking like they were up to no good.
那群青少年在街角可疑地徘徊，看起来像是要做坏事。
He's always sneaking around; I suspect he's up to no good.
他总是鬼鬼祟祟的；我怀疑他没安好心。
She found her son sneaking out of the house in the middle of the night; he must be up to no good.
她发现她儿子半夜偷偷溜出房子；他肯定没干好事。