My 95 lexus es 300 cut off after a whlie its starts up good then i can be drivein and then it cut off and wonts start up could it be the computer

It is most likely not the PCM (engine computer), but what you should do is bring your vehicle to a local shop and have them check for trouble codes that are stored in the PCM, alerting you of where there might be an issue with the vehicle. This is the first step that should be performed, and maintence records of previous work and part replacement would also be helpful. Do not replace any parts unless you know exactly why that part needs to be replaced.