You might want to use an FFT, but your question isn't very clear.

i am currently using mote modules MTM-CM5000 and MTM-CM3000 for data transmission and recieving along radio for a accelerometer.Output of my accelerometer can be see on oscilloscope which show me all data including voltage ,humidity,radioactivity etc all in graph form on my pc. MTS-EX1000 is also used for voltage amplification purpose.Except to all of these raw data output i only want to know about how to calculate the frequency that my accelerometer is sensing here. Thankx..

Really frequency and not acceleration? Then you either need to do an FFT on the data, or simply measure the time between peaks (you might need some filtering to do that, although you can also enable filtering in the module itself).

Actually i want to calculate frequency for a Parkinson patient.This frequency belongs to a tremor of patient arm.I am still confuse that how after sensing through accelerometer i would be able to calculate or display frequency as output.Major confusion is about the use of accelerometer for my purpose like in present case i get amplified voltage as return from sensor,accelerometer can output current value also.So if i want to calculate frequency which value should my sensor return a current value or a voltage value ?? thanks ...