Yes, the sentence "你最近干嘛?" (Nǐ zuìjìn gàn má?) is a commonly used informal expression in Mandarin Chinese to ask someone what they have been up to lately. It can be translated as "What have you been up to lately?" or "What have you been doing recently?" This sentence is appropriate for a casual conversation with your Chinese teacher or friends. However, if you're speaking in a formal or respectful context, it's better to use a more polite form such as "最近您过得怎么样？" (Zuìjìn nín guò de zěnme yàng?), which translates to "How have you been recently?"