There are several common mistakes to avoid when investing online. One is investing without doing proper research and due diligence on the investment opportunity. This can lead to investing in scams or losing money due to poor investment choices. Another mistake is not having a clear investment strategy or plan, which can lead to impulsive or emotional decisions. It's also important to avoid investing more than you can afford to lose, as well as investing in something you don't fully understand. Additionally, it's important to be aware of fees and expenses associated with online investing, such as trading fees or account maintenance fees, and to consider these when making investment decisions.