The Frog is a Good Luck Symbol
When the frog jumps into your life it may indicate now is a time to find opportunities in transition. The frog undergoes incredible transformations to reach the destination of full adulthood, and so do we as humans.
In ancient Egypt Frog-headed Heket was the goddess of birth. As a Celtic symbol meaning, the Frog was deemed lord over all the earth, and the Celts believed it represented curative or healing powers because of its connection with water and cleansing rains.
Other Western traditions focus on the Frog's three stages of development (egg, tadpole, fully formed amphibian) to symbolize resurrection and spiritual evolution.
In China the Frog is an emblem of Yin energy and thought of as good luck. Feng Shui practices recommend putting an image of a Frog in the east window of your home to encourage a happy family life.
Frogs are good luck symbols in Japan, especially for travelers. Images or charms were worn during long voyages to assure safety (particularly across water).
The Japanese word for frog is "kaeru." It is the same word meaning "return." Travelers carry a small frog amulet with the intent of returning safely home.
Here's a mildly interesting video showing the transformation process of the frog.
(adapted from http://www.whats-your-sign.com/animal-symbolism-frog.html)