Most ETFs are quite safe because most of them are index funds. An index ETF is simply a fund that invests in exactly the same securities as a given index, such as the S%26P 500, and tries to match the index's return every year. While all investments involve risks and index funds are exposed to total market volatility, meaning that if the index loses value, the fund follows suit, the general trend of the stock market is upward. Over time, indices are more likely to gain value, so do the ETFs that track them.
There are some risks associated with trading ETFs, but that's the case with any instrument you want to invest in. By their nature, ETFs tend to be low-risk, thanks to diversification and their lower costs. You just have to consider potential risks, such as tax inefficiency, low liquidity, trading fees or choosing the wrong ETF. Both mutual funds and ETFs are considered low-risk investments compared to carefully selected stocks and bonds.
While investing in general always involves a certain level of risk, both mutual funds and ETFs have approximately the same level. It depends on the individual mutual fund and the ETF you're investing in.