Is it necessary to learn acoustic guitar to learn electric guitar?

Agreed you can hop straight onto the electric guitar if you want. It really depends on your preference if you want to play cool riffs and rock it out with that cool electric sound on the guitar. Though many people tend to get acoustic before they go onto electric because acoustic guitars are more challenging to play physically on your fingers. You are having to press down harder on the strings and also it's harder to sound decent on an acoustic than on electric as you can simply cover up mistakes when you're playing a particular tune. Being able to play electric guitar is made simpler by learning acoustic.

You will find that each guitar is a different animal. Each has its pros and cons but it depends on what style you are going for. To answer your question, it is not at all necessary to play acoustic first before electric. There are just more details to look for when buying an electric such as pickups, wood, brand, hardware, amplifier, cables, etc. I have to disagree with some of the answers above, being that the electric is no easier to play than the acoustic: you will find that there are things that don't sound as good on an electric as an acoustic and vice versa. For instance, it is much easier to tap on an electric and sounds better. Conversely, finger style playing tends to flow and sound better on an acoustic than an ESP electric with super hot EMG pickups (due-to-the-fact that these are high gain output pickups most used in heavy rock and metal applications). I hope this helps.
Source: I have been playing for 22 years.

Not at all, in some ways its easier, the fretboard is usually a little
Smaller and normally the string gauge and tension
Is easier on the fingers.
The main drawback is the cost, electrics normally
Cost a little more and you will need an amplifier
And a cable to get started.