This is fine. Your main goal for your reserve funds is preservation of principle, which will limit you to things like:
* money market accounts (not money market funds, they're different since they can "break the buck").
* CDs (not brokered CDs, they can lose principle).
* short-term Treasuries such as notes and bills. You may be OK buying bonds if you hold them to maturity, but nobody can guarantee the future and you may be forced to redeem the bond early.
Nowadays you also need to be careful with normal CDs sold by banks, since some "creative" institutions have started to impose early-redemption penalties in the form of loss of principle. Normally the penalty is loss of some accumulated interest. Read the fine print.
You may be able to get better interest rates at credit unions. Deposits up to $250,000 at federally insured credit unions are protected (similar to FDIC insurance offered by banks). Some financial institutions also offer additional insurance to protect deposits up to $500,000.
If your reserves exceed the insurance limits, some banks offer a program known as
CDARS. It allows you the convenience of keeping all of the deposits in one place, but the offering bank will actually be spreading them around to other banks to remain within the FDIC limits.
The rule of thumb in investing is that there is always a tradeoff between safety and return. If you find an investment that offers a rate of return that is out of line with the norms, be very suspicious.