Is it safe to run a standard DC motor with 3-4 Amps?
It depends on the motor. If you mean a small 130 size motor, then no. Otherwise, provide some more information so that someone can help you out.
Also if you mean directly from the Arduino output, then no as well!
You need to give more information.
Weedpharma
Hi,
What voltage is the motor and what current is the motor rated at.
Just saying running something on 3 to 4 amps, means nothing.
Tom.... 
Just saying running something on 3 to 4 amps, means nothing.
If nothing else it says that you cannot run it directly from the Arduino.
lots of different dances, lots of different music.....
first YES, you can power a standard DC motor with 3-4 amps, by why so little ? why not 20 amps ?
a standard 5 hp, DC motor, 180volts, 25 amps is something you can run from your Arduino.
but the standard DC motor from my son's Thomas the Tank Engine set runs on 1.2 volts an mA's of power.
and, yes, the Arduino can control that as well.
by now you should realize that you only gave half the information.
the motor uses both volts and amps. neither of which the Arduino cares about.
YOU on the other hand, care greatly bout both of those !
first of, you should have gathered that you NEVER try to use power from a pin as the supply to a motor.
you ALWAYS drive something, a transistor, an FET, a relay, a motor speed controller, a motor driver, or some other thing that uses mA of current but acts as the switch for the hundreds or thousands or fractions of an amp that the motor uses.
based on your question, we can gather that you really want to know HOW to drive a 4 amp motor using an Arduino.
for that, you need to outline the motor and application.
will it be speed controlled like a trane or car ? will it be on/off like a water pump ?
did you buy or already have the motor ? if so, please send data sheet of photo of the motor and nameplate if one exists.
bottom line is YES, the caveat is 'with the correct circuit'
and for that, we are here and eager to help !