Is opportunity costs the same as variable costs?

No, the two are very different. Opportunity cost is the cost of a decision made that is considered the value of an alternative that is forgone. For example, if there is a choice between using a car and selling it, the opportunity cost would be the sale price of that car forgone. On the other hand, variable cost would be things like electricity bills, gas bills, the cost of grocery, etc. These are considered variable costs because what you pay each month may vary, based on consumption.