There are many ways, I suggest a few:

1. use a discrete band-filter (using operational amplifier) to filter the frequency you want to measure. Add a bridge to get a direct voltage that is proportional to the alternating input voltage of desired frequency. Sample the voltage with AD converter and display it proportionaly on LCD.
(low AD value - short bar, high AD value - long bar on LCD sisplay)

2. use a digital filtering so that you sample the unfiltered input voltage. By mathematical computation you get the value of desired frequency that you display on LCD. (desired frequency can be selected only by changing the filter coefficients - a digital value used in the computation). Very sutable for such application and single frequency measurement is a GOERTZEL algorithm, that can be implemented even on 8051 with low RAM resources and low computing power. I suggest you try it, if you are an experienced 8051 developer and programmer.

3. try to find a ready made project somewhere on the internet with the schematics and software if existing.