CMCON = 7 will disable the comparators. Also place a small 0.1 or 0.01uF cap between the PIC gnd & vcc pins. Make sure it's as close as possible to the pins.

It's also a good idea to include at least the minimum config options in your code so you're not left with whatever the default unprogrammed config bits are.

I would use at least @ device pic16F628A, intrc_osc_noclkout, wdt_on, mclr_on, lvp_off, protect_off.

If that doesn't take care of it, check your power supply.