How much power can electrical noise (EMI) produce?
Yes, because an optocoupler is as sensitive as any other piece of electronic maybe even more sensitive since the led voltage of the optocoupler is less than CMOS treshold.
To solve the problem:


A resistor between the signal line and GND. Value between 100 and 900K. 
A capacitor between the signal line and GND. Value between 0.1 and 0.47uF.
A resistor in serie with the signal input. Value +- 1K.