Je pensais justement à toi.

Pensais is the imperfect form of penser. In this sentence, French uses the imperfect to describe something that was already going on in the past:

• Je pensais à toi = I was thinking about you / I was thinking of you

If you said J’ai pensé à toi, that usually sounds more like:

• I thought about you
• a completed action, often at a specific moment

So Je pensais justement à toi gives the feeling of I was just thinking about you at that moment.

Here, justement means something like:

• just
• exactly
• as it happens
• actually, at that very moment

So the sentence has the sense of:

• I was just thinking about you
• I was actually thinking about you right then

It adds the idea of a coincidence or perfect timing.

Because French uses two different patterns with penser:

• penser à + person/thing = to think about someone/something
• penser de + person/thing = to think of someone/something in the sense of having an opinion

So:

• Je pensais à toi = I was thinking about you
• Que penses-tu de lui ? = What do you think of him?

That is a very common learner question, because English uses think of/about in overlapping ways, but French separates these meanings more clearly.

Because penser takes the preposition à when it means to think about. So the full structure is:

• penser à quelqu’un

After a preposition like à, French uses a stressed pronoun, not a direct object pronoun.

So:

• à moi
• à toi
• à lui
• à elle
• à nous
• à vous
• à eux / à elles

That is why you say:

• Je pensais à toi

and not:

• Je te pensais (which would not mean the same thing and sounds wrong for this idea)

Toi is the informal singular stressed pronoun, used with:

• friends
• family
• children
• people you address with tu

If you were speaking formally, or to more than one person, you would use vous:

• Je pensais justement à vous.

So the choice between toi and vous depends on the relationship and level of formality.

Yes, it is very natural.

It is a common and idiomatic French sentence. Other natural variations include:

• Je pensais à toi, justement.
• Justement, je pensais à toi.

All of these are natural, but the emphasis shifts slightly:

• Je pensais justement à toi = smooth, neutral
• Je pensais à toi, justement = a bit more emphasis on the coincidence
• Justement, je pensais à toi = stronger emphasis on as it happens

They do not mean the same thing.

• penser à toi = to think about you
• parler de toi = to talk about you
• rêver de toi = to dream about you

French verbs often require a specific preposition, and it is not always the same one English uses. So with penser in this meaning, you must learn:

• penser à quelqu’un / quelque chose

not de.

A careful pronunciation would be approximately:

zhuh pahn-SAY zhyu-stuh-MAH ah TWA

A few useful points:

• Je sounds like zhuh
• pensais ends with the -ais sound, like eh
• justement has a nasal ending: -ment sounds like mahn
• à toi is pronounced smoothly together

In normal speech, it often flows quite a lot:

• Je pensais justement à toi
• almost like: j’pensais justement à toi

Sometimes in context, yes, but its most direct meaning is:

• I was just thinking about you

The imperfect pensais often describes an ongoing background action. Depending on context, English might translate it in slightly different ways:

• I was thinking about you
• I was just thinking about you
• I’d just been thinking about you

But if you are learning the core meaning, the safest translation is:

• I was just thinking about you

No. That is not natural French.

French does not usually form continuous tenses the way English does with was thinking. Instead, it normally uses the imperfect:

• Je pensais à toi

So where English says I was thinking, French often simply uses:

• je pensais

not j’étais pensant.

Toi is a stressed pronoun (also called a disjunctive pronoun).

French uses stressed pronouns:

• after prepositions: à toi
• for emphasis: Moi, je sais
• when standing alone: Qui veut venir ? — Moi.

In this sentence, it is used because it follows the preposition à.

Yes. The structure stays the same:

• Je pensais justement à Marie.
• Je pensais justement à mon frère.
• Je pensais justement à ce problème.

So the pattern is:

• Je pensais justement à + noun/pronoun

This is a useful model to remember.