We would have to see the processing code to help...

2. import guru.ttslib.*;
3. 
   
4. TTS tts;
5. 
   
6. void setup() 
7. {
8. size(100, 100);
9. tts = new TTS();
10. }
11. void draw() 
12. {
13. background(204);
14. if (key == 'c')
15. {
16.   // speak "jravis"
17.  //this sends a single key-stroke of 'c' from speech macros
18.  tts.speak("hELLO!SAURABH");
19. }
20. if (key == 's')
21. {
22.   //Ask "how are you"
23.  //this sends a single key-stroke of 's' from speech macros
24.   tts.speak("I'm doing good. What about you?");
25. }
26. if (key == 'a')
27. {
28.   //tell-"Got my exams tomorrow"
29.  //this sends a single key-stroke of 'a' from speech macros
30.   tts.speak("BEST of LUCK dex!");
31. }
32. }

Once key is set to something, it keeps that value until changed. And thus it will continuously trigger things.

The solution is to set key to something else at the end of draw().

Thanks it worked

" The solution is to set key to something else at the end of draw()."
Or just to use the keyPressed() function instead.
Using key state in draw() is OK in games where you might want to keep a key pressed to move a sprite, but to manage events, the function called when the user does something is better.