Depends a lot on your country, and your work. Where I live, it’s not normal, but I know a number of people who’ve done it, and it’s not really frowned upon.
Is it a quiet time at your workplace, or are things hectic? Are there quiet times and busy times for your team (for instance, if you’re in an accounting team, the end of financial year is very busy), and are you picking a quiet time? Will it be easy for your workplace to cover your workload while you’re away? Is there someone who could do your work, and who needs to be given a chance? Are they short of money, so you taking unpaid leave could actually help them? Think these things through, and work out how you can approach it so that it doesn’t leave your workplace overwhelmed while you’re away. Try to find positive things for them.