I was told that duration of a floating rate bond is almost equal to its reset frequency. Can someone explain why?

Let's assume it's a forward starting bond. In that case, when you try to compute the duration numerically by bumping the curve by 1bp in parallel, every projected cashflow will be increased by 1bp. However, you will discount these higher cashflows at a higher rate and it turns out that the net effect on your bond price is zero. However, once the first cash flow has fixed, the above doesn't hold anymore. The first cash flow doesn't change anymore, so when you bump the curve by 1bp the discount factors will change, so the net effect will be zero for the cashflows which are projected but haven't fixed but non-zero for that first cash flow. The difference in PV will be roughly equal to the daycount fraction to the first cash flow which will be equal or less than the reset frequency.

What kind of bonds are we talking about here?Currently working on bounds of the duration for bonds with floating coupons but this is more related to commodity bonds then LIBOR based bonds...

In other words, Geist says that PV of the curretnly fixed cashflow is the only one affected by a rate shift. The forward starting ones aren't sensitive.

If you use the search facility on this website you will see that this topic has been discussed several times and that there are important caveats to characterizing floating rate notes so simply. If there is a spread to the note (e.g. LIBOR + X%) then there is more duration than the time to the next reset.

Jomni summarized my description above correctly. I also agree with DavidJn's comment. Basically, the way FRN's are priced is by using a Libor curve to find the forward rates you need, using those predictions to determine the future epxected cash flows, then discounting those back to find the PV. (Which, on a reset date, if there is no spread over Libor, should be equal to par barring some marginal effects not worth talking about). Then repeat the entire exercise with your curve shifted up 1 bps and take the difference of the PV's to get the durations...

Floating rate bonds, are repriced periodically. This means that interest rate risk, which can be expressed as duration, is small.